An Arabi came to the Prophet ﷺ and said, "Messenger of Allah, do you kiss young children? By Allah, we do not kiss them."The Messenger of Allah ﷺ replied, "What can I do if Allah has stripped mercy from your heart?"
حدثنا ابن نمير حدثنا هشام عن أبيه
أتى النبي ﷺ أعرابي فقال يا رسول الله أتقبل الصبيان فوالله ما نقبلهم فقال رسول الله ﷺ ما أملك أن الله عز وجل نزع من قلبك الرحمة
Its isnad is sahih. Bukhari related it, 10/426, no. 5998, Fath, in the Book of Manners. Muslim, 4/1808, no. 2317, in the Book of Virtues, and Tirmidhi, 3/212, no. 1911, in the Book of Righteousness, and he said, hasan sahih. This has already appeared in the Musnad of Ali, that the Prophet ﷺ used to kiss Hasan, and Uyayna bin Hisn saw him doing so.