Musannaf Ibn Abi Shayba 37:258

Ya'la ibn 'Ubayd narrated to us, from Musa al-Juhani, from Salih ibn Arbad al-Nakha'i, who said: Umm Salama said: Al-Husayn entered upon the Prophet, may Allah bless him and grant him peace, while I was sitting at the door. I looked in and saw something in the palm of the Prophet, may Allah bless him and grant him peace, which he was turning over, while he [al-Husayn] was sleeping on his stomach. I said: "O Messenger of Allah, I looked in and saw you turning something over in your palm, while the child is sleeping on your stomach and your tears are flowing." He said: "Gabriel came to me with the soil upon which he will be killed, and he informed me that my nation will kill him."