Mahmud bin al-Rabi' (may Allah be pleased with him) says: I remember that the Prophet (peace and blessings be upon him) rinsed his mouth from the bucket of our house (and spat the water out). Mahmud bin al-Rabi' (may Allah be pleased with him) says that Itban bin Malik (may Allah be pleased with him) narrated to me that he said to the Messenger of Allah (peace and blessings be upon him): "My eyesight has gone, and when it rains, the water in the valley becomes an obstacle between me and the mosque. If you (peace and blessings be upon him) would pray in my house, I would take that (spot) as a place of prayer." The Prophet (peace and blessings be upon him) said: "Very well." The next morning the Prophet (peace and blessings be upon him) and Abu Bakr (may Allah be pleased with him) came and asked permission, and both were given permission. He (peace and blessings be upon him) did not sit down; rather he (peace and blessings be upon him) said: "Where would you like me to pray in your house?" I pointed to a corner. The Prophet (peace and blessings be upon him) went forward and we formed rows behind him (peace and blessings be upon him), and he (peace and blessings be upon him) led us in two rak'ahs of prayer. And we held back the Prophet (peace and blessings be upon him) for a dish (jashishah) that we had prepared for him (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5158
(a) Ubaydullah bin Abdullah bin Utbah narrates from his father: I came to Umar bin al-Khattab (may Allah be pleased with him) at midday. I found him offering voluntary prayer, and I stood behind him, so he took hold of me and placed me on his right side. When he came, I moved back in accordance with him, and we formed a row behind Umar (may Allah be pleased with him).
(b) It is reported from Umar and Ali (may Allah be pleased with them both) that when there were three, two would stand behind (the imam).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5159