Musnad Ahmad 938:45

Yahya ibn Sa’id narrated to us, from Hisham, Qatadah narrated to us, from Anas, from Zayd ibn Thabit. And [via] Yazid, he said: Hammam informed us, from Qatadah, from Anas, from Zayd ibn Thabit. And [via] Waki’, al-Dastawa’i narrated to us, from Qatadah, from Anas, from Zayd ibn Thabit, who said: "We ate suhur with the Messenger of Allah, peace and blessings of Allah be upon him, then we went out to the mosque, and the prayer was established." I said: "How much was between them?" He said: "The amount of what a man reads fifty verses." Yazid said in his hadith: I said to Zayd: "How much was the amount of what was between them?" He said: "About fifty verses."