Musnad Ahmad 30:1359

Yunus narrated to us, Layth narrated to us, from Muhammad—meaning Ibn ‘Ajlan—from Suhayl ibn Abi Salih, from his father, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Two will not be gathered in the Fire in a gathering that harms one of them: a Muslim who killed a disbeliever, then the Muslim acted rightly and followed the straight path. And two will not be gathered in the interior of a servant: dust in the way of Allah, and the smoke of Hell. And two will not be gathered in the heart of a servant: faith and stinginess."