THE PRAYER (SALAT)

414.According to Utham, may Allah be pleased with him, the blessed Prophet (peace be upon him) said: 'To perform the late evening Prayer, (Isha), in congregation is equivalent to spending half the night in vigil, while to perform the dawn Prayer, (Fajr), in congregation is like keeping vigil throughout the night. (Muslim).
(Inner Dimensions of Islamic Worship. by Al-Ghazali). (Translated by Muhtar Holland).