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