Silsilat al-Ahadith al-Sahihah

The Messenger of Allah (peace and blessings be upon him) said: "Whoever performs prayers in congregation for forty days, catching the first Takbir (i.e., Takbir al-Tahrimah) with the Imam, two freedoms will be written for him: freedom from Hell and freedom from hypocrisy." This hadith is narrated from Sayyiduna Anas, Sayyiduna Abu Kahil, and Sayyiduna Umar ibn Khattab (may Allah be pleased with them).