The Messenger of Allah ﷺ stood up to pray, and we stood with him. While in the prayer, an Arabi said, "Allah, have mercy on me and on Muhammad, and do not extend Your mercy to anyone else with us."When the Messenger of Allah ﷺ finished with the salam, he said to the Arabi, "You have restricted something vast," meaning the mercy of Allah .
أخبرنا كثير بن عبيد قال حدثنا محمد بن حرب عن الزبيدي عن الزهري عن أبي سلمة
قام رسول الله ﷺ إلى الصلاة وقمنا معه فقال أعرابي وهو في الصلاة اللهم ارحمني ومحمدا ولا ترحم معنا أحدا فلما سلم رسول الله ﷺ قال للأعرابي لقد تحجرت واسعا يريد رحمة الله عز وجل
[Its isnad is sahih] Bukhari narrated it in the Book of Manners, chapter on mercy to people and animals, no. 6010, from the hadith of Zuhri, through the same route, and he explicitly stated that he heard it. It is also found in Kubra, no. 1139, 554, where he said, "Sufyan Ibn Uyayna differed from him."