Musannaf Ibn Abi Shayba 36:110

Khalid ibn Makhlad narrated to us, he said: Abd al-Rahman ibn Abd al-Aziz narrated to us, he said: Al-Zuhri narrated to us, he said: Abu Bakr ibn Abd al-Rahman ibn al-Harith ibn Hisham al-Makhzumi narrated to me, he said: The Negus summoned Ja'far ibn Abi Talib and gathered for him the heads of the Christians. Then he said to Ja'far: "Recite to them what you have with you of the Quran." So he recited to them: "Kaf-Ha-Ya-'Ayn-Sad." Their eyes overflowed, and it was revealed: "You see their eyes overflowing with tears because of what they have recognized of the truth."