Ibn Hisham's Sīrah (better known in English as the Life of Muhammad), describes the exploits of Yūsuf Dhū Nuwās. Ibn Hisham explains that Yūsuf was a convert Jew who grew out his sidelocks (nuwās) and became known as "he of sidelocks." Reportedly, he took power after having killed his predecessor, Dhu Shanatir, with a knife hidden in his shoe.^[3] The historicity of Dhū Nuwās is affirmed by Philostorgius and by Procopius (in the latter's Persian War). Procopius writes that in 525, the armies of the Christian Kingdom of Aksum of Ethiopia invaded ancient Yemen at the request of the Byzantine emperor Justin I to take control of the Himyarite Kingdom, then under the leadership of Yūsuf Dhū Nuwās, who rose to power in 522, probably after he assassinated Dhu Shanatir.

Ibn Hisham explains the same sequence of events under the name of "Yūsuf Dhū Nuwās." Following this invasion, the supremacy of Judaism in the Kingdom of Ḥimyar, as well as in all of Yemen, came to an abrupt end. Imrū' al-Qays, the famous Yemeni poet from the same period, in his poem Taqūl Lī bint al-Kinda Lammā ‘Azafat, laments the death of two great men of Yemen, one of them being Dhū Nuwās, and regards him as the last of the Himyarite kings:

Art thou not saddened how fate has become an ugly beast,
the betrayer of its generation, he that swalloweth up people? It has removed Dhū Nuwās from the fortresses
who once ruled in the strongholds and over men
^[a]

One Syriac source appears to suggest that the mother of Dhū Nuwās may have been a Jew hailing from the Mesopotamian city of Nisibis.^[4][b] If so, that would place her origins within the Sassanid imperial sphere and would illuminate possible political reasons for his later actions against the Christians of Arabia, who were natural allies of the Byzantine Empire.^[4]

Many modern historians, except for Christopher Haas, have argued that her son's conversion was a matter of tactical opportunism since Judaism would have provided him with an ideological counterweight to the religion of his adversary, the Kingdom of Aksum and it also allowed him to curry favour with the Sasanian emperor.^[5]

According to Ibn Ishaq, a king of Himyar, Dhu Nuwas, had burned the Christians in Najran, and an invading army from Aksum (Habasha) occupied Yemen. Dhu Nuwas decided to kill himself by drowning in the sea. Arab tradition states that Dhu Nuwas committed suicide by riding his horse into the Red Sea. The Himyarite Kingdom is said to have been ruled by the Du Yazan dynasty of Jewish converts as early as the late 4th century.^[5]

According to a number of medieval historians, who depend on the account of John of Ephesus, Dhu Nuwas announced that he would persecute the Christians living in his kingdom because Christian states were persecuting his fellow co-religionists in their realms. A letter survives written by Simon, the bishop of Beth Arsham in 524 CE, and recounts the persecution of Dimnon, who is probably Dhu Nuwas, in Najran, Arabia.^[6]

Based on other contemporary sources, Dhu Nuwas, after seizing the throne of the Ḥimyarites around 518 or 523, attacked Najran and its inhabitants, captured them and, burned their churches. The destruction fell out on Tuesday, during the 15th day of the lunar month Tishri, in the year 835 of the Seleucid era counting (corresponding with year 524 CE).^[7][8] After accepting the city's capitulation, he massacred its inhabitants who would not renounce Christianity. Earlier, the Himyarite monarch had attacked and killed the Abyssinian Christians who had settled in Zafar.

According to the Arab historians, Dhu Nuwas then proceeded to write a letter to the Lakhmid king Al-Mundhir III ibn al-Nu'man of al-Ḥīrah and King Kavadh I of Persia to inform them of his deed and to encourage them to do likewise to the Christians under their dominion. Al-Mundhir received the letter in January 519 [sic], as he was receiving an embassy from Constantinople seeking to forge a peace between the Roman Empire and al-Ḥīrha.^[9] He revealed the contents of the letter to the Roman ambassadors, who were horrified by its contents. Word of the slaughter quickly spread throughout the Roman and Persian realms, and refugees from Najran even reached the court of Roman Emperor Justin I himself and begged him to avenge the martyred Christians.

The name Yūsuf 'As'ar Yath'ar, which is believed to be Joseph Dhū-Nuwas, appears in an old South Arabian inscription.^[10] Related inscriptions from the same period were also deciphered by Jamme and Ryckmans and show that in the ensuing wars with his non-Jewish subjects, the combined war booty (excluding deaths) from campaigns waged against the Abyssinians in Ẓafār, the fighters in ’Ašʻarān, Rakbān, Farasān, Muḥwān (Mocha), and the fighters and military units in Najran, amounted to 12,500 war trophies, 11,000 captives and 290,000 camels and bovines and sheep.^[11]

According to ‘Irfan Shahid's Martyrs of Najran – New Documents, Dhu Nuwas sent an army of some 120,000 soldiers to lay siege to the city of Najran, which siege lasted for six months, and the city taken and burnt on the 15th day of the seventh month (the lunar month of Tishri). The city had revolted against the king and refused to deliver itself to the king. About 300 of the city’s inhabitants surrendered to the king’s forces under the assurances of an oath that no harm would come to them, and they were later bound. Those remaining in the city were burnt alive within their church. The death toll in that account is said to have reached about 2000. However, the Sabaean inscriptions describing the events report that by the month of Dhu-Madra'an (between July and September), there had been "1000 killed, 1500 prisoners [taken] and 10,000 head of cattle."^[12]

Jacques Ryckmans, who deciphered the Sabaean inscriptions, writes in his La persécution des chrétiens himyarites that Sarah'il Yaqbul-Yaz'an was both the tribal chief and the lieutenant of King Yusuf 'As'ar during military campaign, he was sent out by the king to take the city of Najran, and the king watched for a possible Abyssinian/Ethiopian incursion along the coastal plains of Yemen near Mokhā (al-Moḫâ) and the strait known as Bāb al-Mandab. It is to be noted that the Ethiopian church in Ẓafar, which had been built by the Himyarite King some years earlier after the proselytizing mission of Theophilos the Indian and another church built by him in Aden (see: Ecclesiastical History of Philostorgius, Epitome of Book III, chapter 4), had been seen by Constantius II during the embassage to the land of the Ḥimyarites (Yemen) around 340 CE. This church was set on fire and razed to the ground, and its Abyssinian inhabitants killed. Later, foreigners (presumably Christians) living in Haḏramawt were also put to death before the king’s army advanced to Najran in the far north and took it.

King Yusuf Asar Yathar, described in an inscription as "king of all nations," had led the major tribes of Yemen (Hamedan, Madh'hij, Kinda, Murad) and successfully defeated the Abyssinian forces in Ẓafâr, Mokhā and Najran. Dhi Yazan leader, Samu Yafa' (سميفع أشوع), become the successor of Yusuf in 527 and the Abyssinian forces led by Abraha had invaded Yemen again in 531.^{[citation needed]}

Najran inscription (518 CE):^[13][14]

The first line :
Sabaean: ليبركن الن ذ لهو سمين وارضين ملكن يوسف اسار يثار ملك كل اشعبن وليبركن اقولن
Arabic: ليبارك الله الذي له (ملك) السماوات والأرض الملك يوسف أسار يثأر ملك كل الشعوب وليبارك الأقيال

God who owns the heavens and the earth bless king Yusuf Asar Yathar, king of all nations and bless the Aqials

Third line:
Sabaean: خصرو مراهمو ملكن يوسف اسار يثار كدهر قلسن وهرج احبشن بظفر وعلي حرب اشعرن وركبن وفرسن
Arabic: الذين ناصروا سيدهم الملك يوسف أسأر يثأر عندما أحرق الكنيسة وقتل الأحباش في ظفار وعلى حرب الأشاعرة وركبان وفرسان

Who they stand with their master, King Yusuf Asar Yathar, when he burned the church and killed the Habashah (Abyssinians) in Dhofar and war on (Habashah) in Ash'aran and Rakban (regions) and Farasan

Fifth line:
Sabaean: وكذه فلح لهفان ملكن بهيت سباتن خمس ماتو عثني عشر االفم مهرجتم واحد عشر االفم سبيم وتسعي
Arabic: وقد أفلح الملك في هذه المعركة في قتل 12500 اثناعشر الف وخمسمائة قتيل و11090 أحد عشر ألف وتسعين اسير

The king has succeeded in these battles in the killing of 12,500 and capturing 11,090

Sixth line:
Sabaean: وثتي ماتن االفن ابلم وبقرم وضانم وتسطرو ذن مسندن قيل شرحال ذي يزن اقرن بعلي نجرن
Arabic: وغنم مئتي الف رأس من الابل والبقر والضان وقد كتب هذه المسند القيل شرحال ذي يزن عندما رابط في نجران

Booty of two hundred thousand camels, cows, sheep, and this Misnad (inscription) was written by Shrahal Dhi Yazan when camped in Najran

Seventh line:
Sabaean: بشعب ذ همدن هجرن وعربن ونقرم بن ازانن واعرب كدت ومردم ومذحجم واقولن اخوتهو بعم ملكن قرنم
Arabic: مع شعب همدان والعرب والمقاتلين اليزنيين وأعراب كندة ومراد ومذحج واخوته الأقيال الذين رابطوا مع الملك

With the nation of Hamedan and the Arabs and the Yazaniin fighters and the A'rab ('nomads') of Kinda and Murad and Madh'hij and his brothers the Aqials who camped with the king

Eighth and ninth lines:
Sabaean: ببحرن بن حبشت ويصنعنن سسلت مدبن وككل ذذكرو بذل مسندن مهرجتم وغنمم ومقرنتم فكسباتم
Arabic: على البحر من جهة الحبشة واقاموا سلسلة من التحصينات في باب المندب وجميع الذين ذكروا بهذا المسند قاتلوا وغنموا ورابطوا في هذه المهمة

On the sea from the side of Habashah (Abyssinia) And they set up a series of fortifications in the Bab al-Mandab and all who mentioned in this Musnad they fought and took booty and camped in this mission

Sabaean: اوده ذ قفلو ابتهمو بثلثت عشر اورخم وليبركن رحمنن بنيهمو شرحبال يكمل وهعن اسار بني لحيعت
Arabic: وعادوا في تاريخ ثلاثة عشر وليبارك الرحمن ابناء شرحبال يكمل وهعن واسار بني لحيعت

And they returned in the history of thirteen and Rahman (god) bless Sharhabal Ekml and Wh'an and Asar Bni Lhi't

• Dhu Nuwas, Zur'ah Yusuf ibn Tuban As'ad abi Karib - 1906 Jewish Encyclopedia article.
• Jewish Warriors