Sahih al-Bukhari 414

It is related that Anas said, "When the Prophet, may Allah bless him and grant him peace, came to Madina, he stopped at the upper part of Madina in an area lknown by the name of a clan called the Banu 'Amr ibn 'Awf. The Prophet, may Allah bless him and grant him peace, stayed among them for fourteen nights. Then he sent for the Banu'n-Najjar who came with their swords girded on. It is as if I could see them now, the Prophet, may Allah bless him and grant him peace, on his camel and Abu Bakr riding behind him with the Banu'n-Najjar all gathered around him, continuing until he arrived at the courtyard of Abu Ayyub. He liked to pray wherever he was when the prayer time came. He would even pray in sheepfolds. He ordered the mosque to be built and sent for some of the Banu'n-Najjar saying, 'Banu'n-Najjar, tell me the price of this walled garden of yours.' They said, 'No, by Allah! We ask for no payment except from Allah!" Anas said, "The place I am telling you about contained pagan graves and some ruins and also some palm-trees. The Prophet, may Allah bless him and grant him peace, ordered the graves of the pagans to be dug up, the ruins to be levelled and the palm-trees to be cut down. The palm trunks were lined up to form the mosque's qibla and its two side walls were made of stone. They used to recite rhyming verses while carrying the stones. And the Prophet was with them saying: 'O Allah, there is no good except the good of the Next World so grant forgiveness to the Ansar and the Muhajirun.'" XVII: Praying in sheep-folds