عَنْ أَبِي مُوسَى الْأَشْعَرِيِّ رَضِيَ اللَّهُ عَنْهُ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ إِنَّمَا سُمِّيَ الْقَلْبُ مِنْ تَقَلُّبِهِ إِنَّمَا مَثَلُ الْقَلْبِ كَمَثَلِ رِيشَةٍ مُعَلَّقَةٍ فِي أَصْلِ شَجَرَةٍ تُقَلِّبُهَا الرِّيحُ ظَهْرًا لِبَطْنٍ
It is narrated from Sayyiduna Abu Musa Ash'ari (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: The heart is called "qalb" (in Arabic) because it keeps turning over. The example of the heart is like a feather hanging by the trunk of a tree, which the wind keeps turning over and over.