SHAHIH BUKHARI | Jilid 2 | Bab 13

And knowledge is the act of the heart as it is referred to by the Statement of Allah (جل جلاله), "But He will call you to account for that which your hearts have earned." (V.2:225)

وَأَنَّ الْمَعْرِفَةَ فِعْلُ الْقَلْبِ لِقَوْلِ اللَّهِ تَعَالَى: {وَلَكِنْ يُؤَاخِذُكُمْ بِمَا كَسَبَتْ قُلُوبُكُمْ}