(a) Qatadah narrates from Sayyiduna Anas bin Malik (may Allah be pleased with him) that Zayd bin Thabit (may Allah be pleased with him) told him: I ate the pre-dawn meal (suhur) with the Messenger of Allah (peace and blessings be upon him), then I went out for the prayer. Anas (may Allah be pleased with him) said: I asked Zayd (may Allah be pleased with him): How long was there between the suhur and the prayer? He said: As long as it takes a man to recite fifty or sixty verses.
(b) Imam al-Bukhari (may Allah have mercy on him) narrated this report from Hammam through Amr bin Asim, except that it uses plural wording, that is: they ate the suhur with the Messenger of Allah (peace and blessings be upon him), then stood up for the prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2142