Musnad Abu Ya'la al-Mawsili 149:13

Shayban narrated to us, Harb ibn Surayj narrated to us, he said: Zaynab bint Yazid ibn Rashiq al-Atakiyyah narrated to me that she heard Aisha say: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The previous nations were one hundred nations; if they testified to the goodness of a servant, Paradise became mandatory for him. And my nation is fifty nations among them; if they testify to the goodness of a servant, Paradise becomes mandatory for him." Zaynab said: A man from the ascetics of the people of Sham, who was called Shahr ibn Hawshab, said: "What was the character of the Messenger of Allah (peace and blessings of Allah be upon him), O Mother of the Believers?" She said: "The Quran, O my son." She said: Then Shahr said: "That is sufficient for you. And who can bear the Quran?" She said: "He whom Allah enables to bear it, O my son."