Sahih al-Bukhari 1211
Actions while Praying
If an animal runs away while one is in Salat
Narrated Al-Azraq bin Qais: We were at Al-Ahwaz fighting the Al-Haruriya (tribe). While I was at the bank of a river a man was praying and the reins of his animal were in his hands and the animal was struggling and he was following the animal. (Shu`ba, a sub-narrator, said that man was Abu Barza Al-Aslami). A man from the Khawarij said, "O Allah! Be harsh to this sheik." And when the sheik (Abu Barza) finished his prayer, he said, "I heard your remark. No doubt, I participated with Allah's Messenger (ﷺ) in six or seven or eight holy battles and saw his leniency, and no doubt, I would rather retain my animal than let it return to its stable, as it would cause me much trouble. "