Musnad Ahmad 765:6

He said: It was read to Sufyan while I was a witness, I heard Ma'mar narrating from al-Zuhri, from Abd al-Rahman ibn Azhar, who said: Khalid ibn al-Walid was wounded. "I saw the Messenger of Allah, may Allah bless him and grant him peace, asking about his camp." I said, and I was a boy: "Who will guide me to the camp of Khalid?" "So he came to him while he was wounded, and he sat beside him."