Sayyiduna Anas (may Allah be pleased with him) narrates this saying of the Prophet (peace and blessings be upon him): "If those who stay away from the Isha prayer and the morning prayer (in congregation) knew how great the reward of these two is, they would come to them, even if they had to come crawling."
Imam Ahmad recorded it, and its narrators have been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2145