I say, and with God's success: It is recommended for a man to wash his private parts during ablution, but it is not obligatory; because it is a place of impurity, so he washes it to prevent impurity from spreading in the body. In contrast, for a woman, it is obligatory to wash her external private parts; because it is akin to the mouth, and it must be purified. Maimunah, may Allah be pleased with her, said: "I poured water for the Prophet (peace be upon him) to wash, and he poured with his right hand over his left and washed them, then he washed his private parts, then he struck his hand on the ground and wiped it with the dust, then he washed it, then he rinsed his mouth and inhaled water, then he washed his face and poured water over his head, then he moved aside and washed his feet, then a towel was brought to him but he did not dry himself with it." This is in Sahih al-Bukhari 1: 102. See: Tabyin al-Haqaiq 1: 14, and Majma' al-Anhar 1: 22, and Allah knows best.