Musnad Ahmad 30:1616

Zakariya ibn ‘Adi narrated to us, Baqiyyah informed us, from Buhayr ibn Sa‘d, from Khalid ibn Ma‘dan, from al-Mutawakkil—or Abu al-Mutawakkil—from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever meets Allah not associating anything with Him, and pays the Zakat of his wealth—his soul being pleased with it, seeking reward—and hears and obeys, then for him is Paradise—or he shall enter Paradise. And there are five for which there is no expiation: Shirk (associating partners) with Allah, killing a soul without right, slandering a believer, fleeing on the day of the advance (battle), or a false oath by which he seizes wealth without right."