From Sahih Muslim (Hadith 1016):
Jabir b. Samura reported:The people of Kufa complained to Umar b. Khattab about Sa'd and they made a mention of his prayer. 'Umar sent for him. He came to him. He ('Umar) told him that the people had found fault with his prayer. He said: I lead them in prayer in accorance with the prayer of the Messenger of Allah (ﷺ). I make no decrease in it. I make them stand for a longer time in the first two (rak'ahs) and shorten it in the last two. Upon this 'Umar remarked: This is what I deemed of thee, O Abu Ishaq
Reference: Muslim 1016