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.'" (IT)
English reference (IT): Vol. 1, Book 1, Hadith 88 (IT)
Arabic reference (IT): Book 1, Hadith 93 (IT)