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 show mercy to anyone else along with us."When the Prophet ﷺ finished the prayer, he said to the Arabi, "You have restricted something vast," meaning the mercy of Allah.
حدثنا إبراهيم بن خالد حدثنا رباح عن معمر عن الزهري أخبرني أبو سلمة بن عبد الرحمن أن
قام رسول الله ﷺ إلى الصلاة وقمنا معه فقال أعرابي وهو في الصلاة اللهم ارحمني ومحمدا ولا ترحم معنا أحدا فلما سلم النبي ﷺ قال للأعرابي لقد تحجرت واسعا يريد رحمة الله
Its isnad is sahih. It appears in Jami al-Masanid 7:462, taken from this very passage. It has already been given at length under 7254, from the narration of Zuhri from Saeed bin Musayab from Abu Hurairah, containing both this incident and the incident of the Bedouin urinating in the masjid. The urination incident alone has already been given under 7786 and 7787. As for this incident of the supplication, Abu Dawud related it independently, as it is here, under 882, from the narration of Yunus from Zuhri, with this same isnad.