Sahih Muslim Book 4, Hadith Number 1646.

Chapter : Forenoon prayer should be offered when it is sufficiently hot.

Anas b. Sirin reported: I asked Ibn ‘Umar like this (as recorded in the previous Hadith) and he made this addition: “And he (the Holy Prophet) made the end of the night prayer as odd number by one rak’ah.” And there is also (this addition): “Stop, stop, you are bulky.”