It is narrated from Hazrat Ubayy bin Ka'b (may Allah be pleased with him) that once the Holy Prophet (peace and blessings be upon him) said: If people knew the reward of offering the Isha and Fajr prayers in congregation, they would surely participate in them even if they had to come crawling. It is narrated from Hazrat Ubayy bin Ka'b (may Allah be pleased with him) that once the Holy Prophet (peace and blessings be upon him) led the Fajr prayer, and after the prayer, he asked, mentioning some people by name one by one, "Is such and such a person present?" Each time, the people replied, "No." The Holy Prophet (peace and blessings be upon him) said: These two prayers (Isha and Fajr) are the heaviest on the hypocrites. If they knew their reward, they would surely participate in them even if they had to come crawling. ... Then the narrator mentioned the entire hadith.