Al-Kāfi

Hadith 421
fasting
3ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ سَهْلِ بْنِ زِيَادٍ عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ أَنَّهُ سَأَلَهُ عَنِ الرَّجُلِ يَحْتَقِنُ تَكُونُ بِهِ الْعِلَّةُ فِي شَهْرِ رَمَضَانَ فَقَالَ الصَّائِمُ لا يَجُوزُ لَهُ أَنْ يَحْتَقِنَ.
3. A number of our people have narrated from Sahl ibn Ziyad from Ahmad ibn Muhammad from who has said the following: “I once asked him (the Imam) (a.s.), about a man who performs an enema because of an illness in the month of Ramadan. He (the Imam) said, ‘Performing an enema is not permissible when fasting.’”
Source: Shaykh Muḥammad b. Yaʿqūb al-Kulaynī