Ibn al-Qayyim reported: It was said to Hasan al-Basri, may Allah have mercy on him, “O Abu Sa’id, which jihad is best?” Hasan said, “Your jihad against your desires.”
Source: Rawḍat al-Muḥibbīn 1/478
عن ابن القيم وَقَدْ قِيلَ لِلْحَسَنِ الْبَصْرِيِّ رَحِمَهُ اللَّهُ يَا أَبَا سَعِيدٍ أَيُّ الْجِهَادِ أَفْضَلُ قَالَ جِهَادُك هَوَاك
1/478 روضة المحبين ونزهة المشتاقين