Musnad Ahmad 32:42

Isma'il narrated to us, 'Abd al-'Aziz ibn Suhayb narrated to us, from Anas ibn Malik—and he said once: 'Abd al-'Aziz ibn Suhayb informed us, from Anas ibn Malik, who said: "Mu'adh used to lead his people in prayer. Haram entered while he was intending to water his palm trees, so he entered the mosque to pray with the people. When he saw that Mu'adh was prolonging [the prayer], he shortened his prayer and caught up with his palm trees to water them. When Mu'adh finished the prayer, it was said to him: 'Haram entered the mosque.'"