Musnad Ahmad 1013:64

Husayn narrated to us, al-Fudayl—meaning Ibn Sulayman—narrated to us, Muhammad ibn Abi Yahya narrated to us, from al-Abbas ibn Sahl ibn Sa’d al-Sa’idi, from his father, who said: I was with the Prophet, may Allah bless him and grant him peace, at the Trench. He took the pickaxe and dug with it, and he encountered a rock, so he laughed. It was said, "What makes you laugh, O Messenger of Allah, may Allah bless him and grant him peace?" He said: "I laughed at people who will be brought from the direction of the East, in chains, being driven to Paradise."