Musnad Ahmad 1060:9

Zakariya ibn 'Adi narrated to us, Baqiyyah informed us, from Buhayr, from Khalid ibn Ma'dan, that Abu Ruhm al-Sam'i narrated to them, from Abu Ayyub, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever worships Allah, not associating anything with Him, establishes the prayer, gives the zakat, fasts Ramadan, and avoids the major sins, for him is Paradise," or "he shall enter Paradise." He was asked: "What are the major sins?" He replied: "Associating partners with Allah (shirk), killing a Muslim soul, and fleeing on the day of the advance (battle)."