Sahih al-Bukhari Book 78, Hadith 33
The Prophet (ﷺ) took a child in his lap for Tahnik (i.e. he chewed a date in his mouth and put its juice in
the mouth of the child). The child urinated on him, so he asked for water and poured it over the place
of the urine.
I said 'O Allah's Messenger (ﷺ)! Which sin is the greatest?" He said, "To set up a rival unto Allah, though He Alone created you." I said, "What next?" He said, "To kill your son lest he should share your food with you." I further asked, "What next?" He said, "To commit illegal sexual intercourse with the wife of your neighbor." And then Allah revealed as proof of the statement of the Prophet: 'Those who invoke not with Allah any other god)................. (to end of verse)...' (25.68)
Allah's Messenger (ﷺ) used to put me on (one of) his thighs and put Al-Hasan bin `Ali on his other thigh, and then embrace us and say, "O Allah! Please be Merciful to them, as I am merciful to them. "