Sahih Muslim 660 a
The Book of Mosques and Places of Prayer
It is permissible to offer voluntary prayers in congregation, and to pray on hasir (palm-fiber mats), khumrah (small mats), cloth, and other pure things
Thabit reported on the authority of Anas: The Messenger of Allah (ﷺ) came to us and there was none in our house but I, my mother and my aunt Umm Haram. He (the Prophet) said: Stand up so that I may lead you in prayer (and there was no time for prescribed prayer). He led us in prayer. A person said to Thabit: Where stood Anas with him (the Prophet)? He replied: He was on the right side. He then blessed us, the members of the household with every good of this world and of the Hereafter. My mother said: Messenger of Allah (and then, pointing towards Anas, said), here is your little servant, invoke the blessing of Allah upon him too. He then blessed me with every good, and he concluded his blessings for me (with these words): Allah! increase his wealth, and his children and make (them the source of) blessing for him.