Sahih Muslim Book 4, Hadith Number 879.

Chapter : The command to observe prayer with tranquillity and calmness and forbiddance of making gesture with hands and lifting them while pronouncing salutation, and the completing of first rows and joining together well in them.

Abu Sa’id al-Khudri reported: The Messenger of Allah (may peace be upon him) saw people at the end of the mosque, and then the (above-mentioned Hadith) was narrated.