Musnad Ahmad 32:307

Isma'il ibn Ibrahim narrated to us, 'Abd al-'Aziz ibn Suhayb narrated to us—and he said once: 'Abd al-'Aziz ibn Suhayb informed us—from Anas ibn Malik, who said: Mu'adh ibn Jabal used to lead his people in prayer. Haram entered while he intended to water his palm trees, so he entered the mosque to pray with the people. When he saw that Mu'adh had lengthened [the prayer], he shortened his prayer and went to his palm trees to water them. When Mu'adh finished the prayer, it was said to him: "Haram entered the mosque, and when he saw you lengthening [the prayer], he shortened his prayer and went to his palm trees to water them." He said: "He is indeed a hypocrite. Does he hasten away from the prayer for the sake of watering his palm trees?" Haram came to the Prophet, peace and blessings of Allah be upon him, while Mu'adh was with him, and said: "O Prophet of Allah, I intended to water some palm trees of mine, so I entered the mosque to pray with the people. When he lengthened [the prayer], I shortened my prayer and went to my palm trees to water them, and he claims that I am a hypocrite." The Prophet, peace and blessings of Allah be upon him, turned to Mu'adh and said: "Are you a tempter, O Mu'adh? Are you a tempter, O Mu'adh? Do not lengthen [the prayer] for them. Recite: 'Glorify the name of your Lord, the Most High' (Surah Al-A'la), 'By the sun and its brightness' (Surah Ash-Shams), and the like."