Muhammad ibn Abi al-Qasim reported: Fudyal ibn ‘Iyad, may Allah gave mercy on him, said, “By the measure of how small a sin seems to you, such is it enormous to Allah. By the measure of how enormous it seems to you, such is it small to Allah.”
Source: al-Tawbah li-Ibn Abī al-Dunyā 64
عن مُحَمَّد بْن أَبِي الْقَاسِمِ قَالَ قَالَ فُضَيْلُ بْنُ عِيَاضٍ رحمه الله بِقَدْرِ مَا يَصْغُرُ الذَّنْبُ عِنْدَكَ كَذَا يَعْظُمُ عِنْدَ اللَّهِ وَبِقَدْرِ مَا يَعْظُمُ عِنْدَكَ كَذَا يَصْغُرُ عِنْدَ اللَّهِ
64 التوبة لابن أبي الدنيا