Muhammad bin Rmh bin al-Mhajr محمد بن رمح بن المهاجر · The Book of the Sunnah

"The Messenger of Allah (ﷺ) said: 'No one will enter Paradise who has even a mustard-seed's weight of arrogance in his heart, and no one will enter Hell who has even a mustard-seed's weight of faith in his heart.'"

"The Messenger of Allah (ﷺ) said: 'The likeness of the heart is that of a feather blown about by the wind in the desert.'"