Riyad as-Salihin

Abu Hurairah (May Allah bepleased with him) reported: The Prophet (ﷺ) kissed his grandson Al-Hasan bin 'Ali (May Allah bepleased with them) in the presence of Al-Aqra' bin Habis. Thereupon he remarked: "I have ten children and I have never kissed any one of them." Messenger of Allah (ﷺ) looked at him and said, "He who does not show mercy to others will not be shown mercy".

[Al-Bukhari and Muslim].