The Amount of Water for Ablution and Ghusl
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 8
وَقَالَ اَلصَّادِقُ عَلَيْهِ اَلسَّلاَمُ: «إِنَّ اَلرَّجُلَ لَيَعْبُدُ اَللَّهَ أَرْبَعِينَ سَنَةً وَ مَا يُطِيعُهُ فِي اَلْوُضُوءِ لِأَنَّهُ يَغْسِلُ مَا أَمَرَ اَللَّهُ عَزَّ وَ جَلَّ بِمَسْحِهِ.
Imam Jafar ibn Muhammad Al-Sadiq عليه السلام said: "A man may worship Allah سبحانه وتعالى for forty years but does not truly obey Him in wudu (ablution) because he washes what Allah سبحانه وتعالى, Mighty and Majestic, commanded him to wipe."
- Ṣaḥīḥ al-Faqīh