Sahih Al Bukhari Hadith Number 1134

Narrated Qatada: Anas bin Malik said, “The Prophet (peace be upon him) and Zaid bin Thabit took their Suhur together. When they finished it, the Prophet (peace be upon him) stood for the (Fajr) prayer and offered it.” We asked Anas, “What was the interval between their finishing the Suhur and the starting of the morning prayer?” Anas replied, “It was equal to the time taken by a person in reciting fifty verses of the Qur’an.”

19  Prayer at Night (Tahajjud)
Hadith number 1134
Volume no 2
Chapter: 8 (Whoever took the Suhur and did not sleep before offering Fajr prayers)