Abu Sa'eed Al-Khudri narrated that the Messenger of Allah (s.a.w) said:
"Whoever had the weight of a speck of faith in his heart will depart from the Fire." Abu Sa'eed said: "Whoever has doubt then let him recite: Indeed Allah does not deal unjustly with even the weight of a speck." (FR)
English reference (FR): Vol. 4, Book 13, Hadith 2598 (FR)
Arabic reference (FR): Book 39, Hadith 2802 (FR)