It was narrated that Abu Musa Al-Ash'ari said:
"The Messenger of Allah (ﷺ) said: 'The likeness of the heart is that of a feather blown about by the wind in the desert.'" (PT)
English reference (PT): Vol. 1, Book 1, Hadith 88 (PT)
Arabic reference (PT): Book 1, Hadith 93 (PT)