It is narrated from Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) kissed Hasan bin Ali (may Allah be pleased with them both) while al-Aqra' bin Habis (may Allah be pleased with him) was sitting with him. He said: O Prophet of Allah! I have ten sons and I have never kissed any of them. He (peace and blessings be upon him) looked at him and said: "Indeed, whoever does not show mercy will not be shown mercy."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13576
It is narrated from Sayyidah Aishah (may Allah be pleased with her) that a Bedouin came to the Prophet (peace and blessings be upon him) and said: You kiss children? We do not kiss them. He (peace and blessings be upon him) said: "If Allah has removed mercy from your heart, what can I do about it?"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13577
Aishah (may Allah be pleased with her) said: I have not seen anyone who resembled the Prophet (peace and blessings be upon him) more in speech and conversation than Fatimah (may Allah be pleased with her). When she came to him (peace and blessings be upon him), he (peace and blessings be upon him) would welcome her, stand up, take her by the hand, kiss her and seat her in his own place; and when he (peace and blessings be upon him) went to her, she would welcome him (peace and blessings be upon him), stand up, take his (peace and blessings be upon him) hand and kiss it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13578