Sahih al-Bukhari Book 78, Hadith 28
Allah's Messenger (ﷺ) kissed Al-Hasan bin `Ali while Al-Aqra' bin H`Abis at-Tamim was sitting beside him.
Al-Aqra said, "I have ten children and I have never kissed anyone of them," Allah's Messenger (ﷺ) cast a
look at him and said, "Whoever is not merciful to others will not be treated mercifully."
The Prophet (ﷺ) came out towards us, while carrying Umamah, the daughter of Abi Al-As (his granddaughter) over his shoulder. He prayed, and when he wanted to bow, he put her down, and when he stood up, he lifted her up.
A bedouin came to the Prophet (ﷺ) and said, "You (people) kiss the boys! We don't kiss them." The Prophet said, "I cannot put mercy in your heart after Allah has taken it away from it."