Abdullah bin Shaddad bin al-Had narrates from his father (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) came out to us carrying his grandson, Hasan or Husayn (may Allah be pleased with them both). He (peace and blessings be upon him) went forward to lead the prayer and set him down near his right foot. When the Messenger of Allah (peace and blessings be upon him) prostrated and made it very long, I raised my head and saw that the Messenger of Allah (peace and blessings be upon him) was in prostration and the child was riding on his (peace and blessings be upon him) back. I went back into prostration. When the Messenger of Allah (peace and blessings be upon him) finished the prayer with the salam, the people said: "O Messenger of Allah (peace and blessings be upon him)! You made a very long prostration in this prayer; you do not usually prostrate for that long. Were you given some command during the prayer, or was revelation coming to you?" He (peace and blessings be upon him) said: "None of that happened. Rather, my son was riding on me, and I did not like to hurry so that he could not fulfil his wish."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3423
Zirr bin Hubaysh narrates: One day the Messenger of Allah (peace and blessings be upon him) was leading the people in prayer when Hasan and Husayn (may Allah be pleased with them both) came, and they were both young boys. They climbed onto the back of the Messenger of Allah (peace and blessings be upon him) while he was in prostration. The people turned towards them to move them away from doing that. He (peace and blessings be upon him) said: "Leave them, may my father and mother be ransomed for them. Whoever loves me, let him love these two."
Imam al-Bayhaqi (may Allah have mercy on him) said: Sayyiduna Anas bin Malik (may Allah be pleased with him) said: I have not seen anyone more compassionate and kind towards children than the Messenger of Allah (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3424
The hadith reported from Sayyiduna Anas (may Allah be pleased with him) is in Sahih Muslim, and it is recorded in the book of Imam Muslim, together with all the reports describing the excellent character of the Messenger of Allah (peace and blessings be upon him) and his beautiful qualities, which whoever recognises would not find unlikely what we have mentioned in these two chapters, namely his kindness and mercy, along with the saying of Allah Almighty: "To the believers he is kind and merciful." [Surah al-Tawbah: 128]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3425