Zainab bint Jahash, the wife of the Holy Prophet (S), that she says: One day the Prophet (S) was sleeping in my house when Imam Husayn (a.s.) entered therein. I tried to keep him busy so that he would not wake up the Prophet (S) from his sleep. Then I became engrossed in some work and Husayn entered the room wherein the Prophet was sleeping. I followed him and saw that he was lying on top of the Holy Prophet (S) and urinated on his stomach. I tried to lift him up, but the Prophet (S) said,
“O Zainab! Leave him alone until he finishes.”
When he finished, the Prophet (S) arose and purified himself and started reciting the Prayers (Salat). As soon as he went into prostration (Sajdah) Husayn sat on his back. The Prophet remained in prostration until Husayn himself got off from his back. Then when he arose Husayn returned back and the Prophet lifted him up. When he finished his Prayers he stretched his hands forward and said, “Come near, come near O’ Jibra’eel.” I asked, “O Messenger of Allah! Today I found you doing something which you have never done before.” To which the Prophet replied,
“Yes, Jibra’eel came to offer condolences and told me that my people would kill my Husayn, and he brought along with him red sand for me.”
Reference : Nafasul Mahmoom – Shaikh abbas Qummi (r.a.)