Musnad Ahmad 907:25

Husayn ibn Muhammad narrated to us, Ayyub—meaning Ibn Jabir—narrated to us, from Simak, from Jabir ibn Samurah, who said: "The Messenger of Allah (ﷺ) used to lead us in the obligatory prayer, and he would neither lengthen it nor shorten it; it was moderate between that. And he used to delay the night prayer (al-'atamah)."