Musnad Ahmad 27:1745

Sulayman ibn Dawud al-Hashimi narrated to us, Isma'il informed us, Musa ibn 'Uqbah informed me, from Salim ibn 'Abd Allah, from his father: "The Prophet, peace and blessings of Allah be upon him, was approached while he was at his resting place in Dhu al-Hulayfah, in the bottom of the valley. It was said to him: 'You are in a blessed valley.'" Musa said: "Salim had us kneel at the place where 'Abd Allah used to have his mount kneel, seeking the resting place of the Prophet, peace and blessings of Allah be upon him, and it is below the mosque that is in the bottom of the valley, between it and the road, in the middle of that."