Sahih Al Bukhari Hadith Number 1167

Narrated Abu Qatada bin Rabi Al-Ansari;: The Prophet (peace be upon him) said, “If anyone of you enters a Mosque, he should not sit until he has offered a tworak` at prayer.”

19  Prayer at Night (Tahajjud)
Hadith number 1167
Volume no 2
Chapter: 28 (What is recited in the two Rak’a (Sunna) of the Fajr)