The Prophet Muhammad had 9 wives and two slave girls at the same time; besides, it is known that he had relations with various women at different times. Even with 9 wives and two slave girls, he sought sexual pleasure with his menstruating wife. During the menstrual cycle, we usually refrain from intercourse and control our desires. Since the Prophet had so many wives and slave girls, he could naturally have gone to another wife and fulfilled his sexual needs at that time. But the Prophet did not leave his wives alone even during that period. He would have a cloth tied over the wife's private parts and use the other parts of her body to fulfill his sexual needs. That is, he certainly rubbed his private parts against her knees, breasts, mouth, and so on. Let us learn this matter from Ahmadullah,

Proof of these matters is found in many hadiths - (( Sahih Muslim, Islamic Foundation, Hadith: 572 )) (( Sunan an-Nasa'i, Islamic Foundation, Hadith: 374 ))

Sahih Muslim (Islamic Foundation)
3/ Menstruation
Section: 1. Mixing with a menstruating woman over the izār
572. Abu Bakr ibn Abu Shaybah (RA), Zuhayr ibn Harb (RA) and Ishaq ibn Ibrahim (RA) ... narrated from Aisha (RA). She said, whenever one of us became menstruating, on the order of the Messenger of Allah (peace be upon him) she would tie a cloth tightly over her lower part. Then the Messenger of Allah (peace be upon him) would mix with her.
Hadith grade: Sahih (Authentic)
Narrator: Aisha bint Abu Bakr al-Siddiq (RA)

Sunan an-Nasa'i (Islamic Foundation)
3/ Regarding Hayd and Istihadah
Section: 12/ Pressing his body against the menstruating wife's body
374. Ishaq ibn Ibrahim (RA) ... narrated from Aisha (RA). She said: whenever one of us became menstruating, the Messenger of Allah (peace be upon him) would order her to put on the izār. Then he would press his body against her body.
Hadith grade: Sahih (Authentic)
Narrator: Aisha bint Abu Bakr al-Siddiq (RA)