Some scholars have imagined that specifying the amount of one mudd of water for ablution is such a determination that it is not permissible to perform ablution with less water than this.

Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) used to perform ablution with one mudd and take a bath with five mudd. Imam Abu Bakr (may Allah have mercy on him) says that the "makook" mentioned in this hadith refers to "mudd" itself.