Abu Huraira related that the Prophet of Allah (SAW) said: Whenever a man sits between the four limbs [shu’ab] of a woman and then exerts her [jahadaha], it is obligatory for him to wash.
- Sahih Muslim, The book of menstruation

Regarding His (SAW) words: Whenever a man sits between a woman’s four limbs [shu’abiha] and then exerts her; in another narration “ash’abiha”. Scholars have differed on the intended meaning of “the four limbs”; it is said that this refers to the two hands and the two legs, or the two legs and the two thighs, or the two legs and the two labia. Al-Qadi ‘Iyad opted for an intended meaning of the four sides of the vagina. The “shu’ab” are the parts; one part is a “shu’ba”, while there are those who say “ashba’ ”, the plural of shu’ab. And the meaning of “exerts her” is to drill her, which is what Al-Khatabi said. Others have said to cause her weariness and discomfort, as in the saying “she exerted him or wore him out, causing him discomfort.” Al-Qadi ‘Iyad (may Allah Most High have mercy on him) said it is more proper for “he exerted her” to mean that he reached his full effort in his task with her, where “effort” means force and capability, and this is an indication of the movement, and can indicate the nature of the task, similar to those who say “he drilled her”, that is, he exhausted her with his movement. Otherwise what discomfort could he produce in that? But Allah knows better.