Riyad as-Salihin 1230
Zaid bin Thabit (May Allah be pleased with him) reported:
We took Suhur (predawn meal) with the Messenger of Allah (ﷺ) 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)‏‏)‏