The two destructive diseases Allāh عز وجل says,   فِي قُلُوبِهِم مَّرَضٌ فَزَادَهُمُ الله مَرَضًا ۖ وَلَهُمْ عَذَابٌ أَلِيمٌ بِمَا كَانُوا يَكْذِبُونَ   “In their hearts is a disease, so Allāh has increased their disease; and for them is a painful punishment because they used to tell lies (to mislead others).” [Qur’ān: Sūrah al-Baqarah, verse no.10]     Imām ‘Abdur Rahmān as-S’adī رحمه الله mentioned regarding the above verse,   And His statement: {In their hearts is a disease},   what is meant by disease here is the disease of doubt, misconceptions, and hypocrisy, because the heart is exposed to two diseases that take it out of its healthy and balanced state: the disease of false doubts, and the disease of destructive desires. So disbelief, hypocrisy, doubts, and innovations (in the religion) are all from the disease of doubts; and fornication, the love of obscene acts and sins, and doing them are from the disease of desires, as Allāh the Most High said:     فَيَطْمَعَ الَّذِي فِي قَلْبِهِ مَرَضٌ .. “so he in whose heart is a disease may be tempted..” [Qur’ān: Sūrah al-Ahzab, verse no.32],   which is the desire for fornication, and the one who is safe and sound is the one who is free from these two diseases, so he attains certainty, faith, and patience (to keep away) from every sin, and thus he rejoices in the cloak of well-being.   ‎—————— [Tayseer al-Kareem ar-Rahmān fee tafseer Kalam al-Mannān, vol.1, pg.40, Dār ibn al-Jawzee print, 6th edition] https://markazmuaadh.com/library/quran/