One of his grandchildren urinated in his lap and he, sallallaahu ‘alayhi wa sallam, did not become angry:

Lubaabah bint Al-Haarith narrated that Al-Hasan ibn 'Ali was sitting in the lap of the Prophet of Allah, sallallaahu 'alayhi wa sallam, and then urinated. She told the Prophet of Allah, sallallaahu 'alayhi wa sallam, "Change your garment, and give me yours so that I can wash it." The Prophet of Allah, sallallaahu 'alayhi wa sallam, said: "Only the urine of a baby girl should be washed, but the urine of a boy should have water sprinkled on it.

Abu Layla said: "I was with the Prophet of Allah, sallallaahu 'alayhi wasallam, and Al-Hasan or Al-Husayn was lying on his chest or stomach. I noticed that he began to urinate, so we stood up to take him. The Prophet of Allah, sallallaahu 'alayhi wa sallam, said: "Leave my son, do not scare him [and leave him] until he finishes urinating." Then he followed it with washing with water and I saw his urine gushing out fast uninterrupted.”