Narrated Anas bin Malik: When Allah's Apostle arrived at Medina, he alighted at the upper part of Medina among the people called Bani `Amr bin `Auf and he stayed with them for fourteen nights. Then he sent for the chiefs of Bani An-Najjar, and they came, carrying their swords. As if I am just now looking at Allah's Apostle on his she-camel with Abu Bakr riding behind him (on the same camel) and the chiefs of Bani An- Najjar around him till he dismounted in the courtyard of Abu Aiyub's home. The Prophet used to offer the prayer wherever the prayer was due, and he would pray even in sheepfolds. Then he ordered that the mosque be built. He sent for the chiefs of Banu An-Najjar, and when they came, he said, "O Banu An-Najjar! Suggest to me the price of this garden of yours." They replied "No! By Allah, we do not demand its price except from Allah." In that garden there were the (following) things that I will tell you: Graves of pagans, unleveled land with holes and pits etc., and date-palm trees. Allah's Apostle ordered that the graves of the pagans be dug up and, the unleveled land be leveled and the date-palm trees be cut down. The trunks of the trees were arranged so as to form the wall facing the Qibla. The Stone pillars were built at the sides of its gate. The companions of the Prophet were carrying the stones and reciting some lyrics, and Allah's Apostle . . was with them and they were saying, "O Allah! There is no good Excel the good of the Hereafter, so bestow victory on the Ansar and the Emigrants. "
USC-MSA web (English) Reference: Volume 5, Book 58, Number 269