While Allah's Messenger (ﷺ) was prostrating (as stated below).

Narrated `Abdullah bin Mas`ud:

Once the Prophet (ﷺ) was offering prayers at the Ka`ba. Abu Jahl was sitting with some of his companions. One of them said to the others, "Who amongst you will bring the Abdominal contents (intestines, etc.) of a camel of Bani so and so and put it on the back of Muhammad, when he prostrates?" The most unfortunate of them got up and brought it. He waited till the Prophet (ﷺ) prostrated and then placed it on his back between his shoulders. I was watching but could not do any thing. I wish I had some people with me to hold out against them. They started laughing and falling on one another. Allah's Messenger (ﷺ) was in prostration and he did not lift his head up till Fatima (Prophet's daughter) came and threw that (camel's Abdominal contents) away from his back. He raised his head and said thrice, "O Allah! Punish Quraish." So it was hard for Abu Jahl and his companions when the Prophet invoked Allah against them as they had a conviction that the prayers and invocations were accepted in this city (Mecca). The Prophet (ﷺ) said, "O Allah! Punish Abu Jahl, `Utba bin Rabi`a, Shaiba bin Rabi`a, Al-Walid bin `Utba, Umaiya bin Khalaf, and `Uqba bin Al Mu'it [??] (and he mentioned the seventh whose name I cannot recall). By Allah in Whose Hands my life is, I saw the dead bodies of those persons who were counted by Allah's Messenger (ﷺ) in the Qalib (one of the wells) of Badr.