Riyad as-Salihin, Book 9, Hadith 1230 (In-Book) ⓘ
Zaid bin Thabit (May Allah be pleased with him) reported: We took Suhur (predawn meal) with the Messenger of Allah and then we stood up for (Fajr) Salat (prayer). It was asked: "How long was the gap between the two?" He replied: "The time required for the recitation of fifty Ayat."[Al-Bukhari and Muslim].
وعن زيد بن ثابت رضي الله عنه قال: تسحرنا مع رسول الله صلى الله عليه وسلم ثم قمنا إلى الصلاة قيل كم كان بينهما؟ قال: خمسون آية ((متفق عليه))