Musnad Ahmad 881:1

'Affan narrated to us, Wuhayb narrated to us, 'Amr ibn Yahya narrated to us, from Mu'adh ibn Rifa'ah al-Ansari, from a man from Banu Salimah who was called Sulaym, who came to the Messenger of Allah, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, Mu'adh ibn Jabal comes to us after we have slept, and we are at our work during the day, so he calls for the prayer, and we go out to him, and he makes it long for us." The Messenger of Allah, peace and blessings of Allah be upon him, said: "O Mu'adh ibn Jabal, do not be a source of trial (fattan). Either pray with me, or make it light for your people." Then he said: "O Sulaym, what do you have of the Quran?" He said: "I ask Allah for Paradise, and I seek refuge in Him from the Fire, and by Allah, I do not understand your murmuring (dandana), nor the murmuring of Mu'adh." The Messenger of Allah, peace and blessings of Allah be upon him, said: "And does my murmuring and the murmuring of Mu'adh amount to anything other than that we ask Allah for Paradise and seek refuge in Him from the Fire?" Then Sulaym said: "You will see tomorrow when the people meet [in battle], if Allah wills." He said: And the people were preparing for Uhud, and he went out and was among the martyrs.