Musnad Ahmad 1153:599

Qutaybah ibn Sa'id narrated to us, he said: 'Abd al-'Aziz ibn Muhammad narrated to us, from 'Alqamah ibn Abi 'Alqamah, from his mother, from 'Aishah, that she said: The Messenger of Allah (peace and blessings of Allah be upon him) went out one night, so I sent Barirah to follow him, to see where he went. She said: So he headed towards Baqi' al-Gharqad, and he stood at the nearest part of the Baqi', then he raised his hands, then he turned away. Barirah returned to me and informed me. When it became morning, I asked him, and I said: O Messenger of Allah, where did you go out tonight? He said: "I was sent to the people of the Baqi' to pray for them."