Musnad Abu Ya'la al-Mawsili 146:9

Ja'far ibn Mihran narrated to us, 'Abd al-Warith narrated to us, from Abu al-Tayyah al-Duba'i, Anas ibn Malik narrated to us, he said: When the Messenger of Allah (peace be upon him) arrived in Medina, he stayed in the upper part of Medina in a neighborhood called Banu 'Amr ibn 'Awf. The Messenger of Allah (peace be upon him) stayed among them for fourteen nights. Then he sent for the notables of Banu al-Najjar, and they came girding their swords. Anas said: It is as if I am looking at the Messenger of Allah (peace be upon him) on his riding beast, with Abu Bakr behind him, and the notables of Banu al-Najjar around him, until he stopped at the courtyard of Abu Ayyub. The Messenger of Allah (peace be upon him) used to pray wherever the prayer overtook him, and he would pray in the sheepfolds. Then he ordered the building of the mosque, so he sent for the notables of Banu al-Najjar, and they came. He said: "O Banu al-Najjar, name me a price for this garden of yours." They said: "No, by Allah, we do not seek its price except from Allah." Anas said: It contained what I am telling you; it contained the graves of the polytheists, it was in ruins, and it had palm trees. The Messenger of Allah (peace be upon him) ordered the graves of the polytheists, so they were dug up; and the ruins, so they were leveled; and the palm trees, so they were cut down. They placed the palm trunks at the qibla of the mosque and made its doorposts of stone. He said: They began to transport those rocks while they were chanting rajaz poetry, and the Messenger of Allah (peace be upon him) was with them, and they were saying: "O Allah, there is no good except the good of the Hereafter, so forgive the Ansar and the Muhajirun."