Sahih Muslim Book 4, Hadith Number 1392.

Chapter : Permission to remain away from the congregational prayer for any valid reason.

Maimuna, the wife of the Apostle of Allah (may peace be upon him), reported: The Messenger of Allah (may peace be upon him) said prayer while I was by his side, and at times when he prostrated his cloth touched me, and he prayed on a small mat.