Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: Food for sahur was presented to the Prophet Muhammad (peace and blessings be upon him) and Sayyiduna Zayd bin Thabit (may Allah be pleased with him). When the Prophet (peace and blessings be upon him) finished eating sahur, he got up for the morning prayer. The narrator says: We asked Sayyiduna Anas bin Malik (may Allah be pleased with him) how much time there was between their finishing sahur and beginning the Fajr prayer, so Sayyiduna Anas (may Allah be pleased with him) replied: As long as it takes a person to recite fifty verses.
Hadith Referenceصحیح ابن حبان / كتاب الصلاة / 1497
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «صحيح سنن ابن ماجه» (1694): ق.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط مسلم