The Prophet (may Allah's peace and blessings be upon him) used to take a ritual bath with one Sā‘ up to five Mudds, and he used to perform ablution with one Mudd

The Prophet (may Allah's peace and blessings be upon him) used to take a bath for Janābah (sexual impurity) with one Sā‘ to five Mudds and perform ablution with one Mudd. A Sā‘ equals four Mudds, and a Mudd is the amount that would fill the palms of an average-sized person.

1. It is prescribed to use less water for ablution and ritual bathing and not to use it wastefully, even if water is abundant.
2. It is recommended to use little water for ablution and ritual baths - as needed. This is the guidance of the Prophet (may Allah's peace and blessings be upon him).
3. The bottom line is to perform ablution and take a ritual bath thoroughly while observing the relevant Sunnahs and etiquettes, without extravagance or stinginess. One should take into account the time, the abundance or shortage of water, and so on.
4. Janābah: applies to anyone who has ejaculated or engaged in sexual intercourse. It was called as such because the one in a state of Janābah should keep away (Ijtināb) from prayer and other acts of worship until he is purified from it.
5. Sā‘: a well-known measure. It refers to the Prophetic Sā‘, which weighs 480 Miskals of good wheat, or 3 liters.
6. Mudd: a Shar‘i unit of measurement, which is the handful of a moderate person when he fills his hand with and extends it. Mudd is a quarter of a Sā‘, by consensus among the scholars, and it equals 750 milliliters.

صحيح البخاري (1/ 51) (201). صحيح مسلم (1/ 258) (325). توضيح الأحكام، للبسام (1/ 250). سُبل السلام، للصنعاني (1/ 79 ). فتح ذي الجلال والإكرام، لابن عثيمين (1/ 212). منحة العلَّام، لعبد الله الفوزان (1/ 186). منار القاري شرح مختصر صحيح البخاري، لحمزة قاسم (1/ 272). تحقيق مقدار المد والصاع النبوي، للدكتور عبدالمحسن القاسم