Sahih Al Bukhari Hadith Number 737

Narrated Abu Qilaba: I saw Malik bin Huwairith saying Takbir and raising both his hands (on starting the prayers and raising his hands on bowing and also on raising his head after bowing. Malik bin Huwairith said, “Allah’s Messenger (peace be upon him) did the same.”

10  Call to Prayers (Adhaan)
Hadith number 737
Volume no 1
Chapter: 84 (To raise both hands while saying the Takbir [on opening As-Salat (the prayer)], and while bowing and on raising up the head (after bowing)