Sahih Muslim Book 004, Hadith Number 1088.
Chapter : The virtue of building the mosques and exhortation to it.
'Alqama and Aswad reported that they went to 'Abdullah. He said: Have (people) behind you said prayer? They said: Yes. He stood between them ('Alqama and Aswad). One was on his right aide and the other was on his left. We then bowed and placed our hands on our knees. He struck our hands and then putting his hands together, palm to palm, placed them between his thighs. When he completed the prayer he said: This is how the Messenger of Allah (may peace be upon him) used to do.