Silsilat al-Ahadith al-Sahihah

Sayyiduna Anas (may Allah be pleased with him) narrates that a man was sitting with the Prophet Muhammad (peace and blessings be upon him). His son came to him, so he kissed him and seated him in his lap. After that, his daughter came, and he seated her beside him. The Prophet Muhammad (peace and blessings be upon him) said: "Why did you not do justice between them?"—meaning, you kissed your son but did not kiss your daughter.