Sayyiduna Zayd bin Thabit (may Allah be pleased with him) said: We would take suhur with the Messenger of Allah (peace and blessings be upon him), then stand up for the prayer. I said: How long was the interval between the adhan and the suhur? He said: As long as it takes to recite fifty verses.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8124