وَقَلْبُهُ مُطْمَئِنٌّ بِالْإِيمَانِ
While his heart is tranquil in faith. (Al-Nahl 16:106)
وَلَمَّا يَدْخُلِ الْإِيمَانُ فِي قُلُوبِكُمْ
Faith has not yet entered your hearts. (Al-Hujurat 49:14)
أُولَٰئِكَ كَتَبَ فِي قُلُوبِهِمُ الْإِيمَانَ
Those are the people in whose hearts Allah has inscribed faith. (Al-Mujadilah 58:22)
These verses explicitly connect faith with the heart, emphasizing inner conviction as fundamental.