Musnad Ahmad 33:527

Hassan narrated to us, Zuhayr narrated to us, from Abu al-Zubayr, from Jabir, who said: The Messenger of Allah (peace and blessings of Allah be upon him) sent me while he was setting out toward Banu al-Mustaliq. I came to him while he was praying on his camel, and I spoke to him. He gestured with his hand like this—and Zuhayr gestured with his palm. Then I spoke to him, and he gestured with his hand like this, while I could hear him reciting and nodding his head. When he finished, he said: "What did you do regarding that which I sent you for? For nothing prevented me from speaking to you except that I was praying."