The Prophet used to say: "Whoever performs prayer in congregation at the mosque for forty nights, never missing the first Rak'ah of the 'Isha' prayer, Allah will thereby decree for him salvation from the Fire."
Sunan Ibn Majah Book 4, Hadith 64
← Previous Hadith "The Messenger of Allah said: 'The most burdensome prayers for the hypocrites are the 'Isha' prayer and the Fajr prayer. If only they knew what (reward) there is in them, they would come to them even if they had to crawl.'"

Sunan Ibn Majah Book 4, Hadith 63 Next Hadith → "The Messenger of Allah said: 'When one of you enters the mosque, he is in a state of prayer, so long as the prayer keeps him there, and the angels will send prayer upon anyone of you so long as he remains in the place where he prayed, saying: "O Allah, forgive him; O Allah, have mercy on him; O Allah, accept his repentance," so long as he does not commit Hadath nor disturb anyone.'"

Sunan Ibn Majah Book 4, Hadith 65