Hazrat Ubayy bin Ka'b narrates that the Messenger of Allah, peace and blessings be upon him, once led us in prayer. When he finished the prayer, he noticed that some people were missing from the mosque. Upon this, he said, "Is so-and-so present?" We replied, "Yes." He continued until he had mentioned three men by name. Then he said, "There is no prayer heavier on the hypocrites than the 'Isha and Fajr prayers. If they knew the reward for them, they would come to the mosque even if they had to crawl on their knees."