The Chapter of the Qibla
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 43
وَ رَوَى مُحَمَّدُ بْنُ أَبِي حَمْزَةَ عَنْ أَبِي اَلْحَسَنِ اَلْأَوَّلِ عَلَيْهِ اَلسَّلاَمُ أَنَّهُ قَالَ: «إِذَا ظَهَرَ اَلنَّزُّ مِنْ خَلْفِ اَلْكَنِيفِ وَ هُوَ فِي اَلْقِبْلَةِ يَسْتُرُهُ بِشَيْءٍ.
Muhammad ibn Abi Hamzah narrated from Imam Abu al-Hasan al-Awwal عليه السلام that He said: "If a seepage (liquid or discharge) appears behind a latrine (toilet) and it is in the direction of the Qiblah, one should cover it with something."
- Ṣaḥīḥ al-Faqīh, p. 42