All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
It is desirable for one who has had sex with one of his wives to perform Ghusl if he wants to have sex with another wife. Abu Raafi' reported that the Prophet once had sex with his wives one after the other and had a Ghusl after each intercourse. I (Abu Raafi') said: 'O Allah Messenger! Is not sufficient to have only one Ghusl (or why to have more than one Ghusl)? The Prophet said: “It is more righteous, better and purer (to have Ghusl after each intercourse).” [Abu Daawood and An-Nasaa'i; Al-Albaani graded it as Hasan]
However, according to the majority of the scholars, if one does not perform Ghusl, he is advised to perform ablution. According to the scholars who interpret religious texts according to their literal meaning, and Ibn Habeeb, it is obligatory to perform ablution. They based their opinion on the Prophetic Hadeeth that reads: “Whoever has sex with his wife, and he intends to do again, he has to perform ablution before the second time.” [Muslim]
Anyway, we think that the opinion of the majority of the scholars is the preponderant opinion for the Hadeth that reads: “That performing ablution will make one more active.”
Another Hadeeth from ‘Aa’ishah reads: “The Prophet used to have sex more than one time without performing ablution.” [At-Tahawi]
However, the above-mentioned Hadeeth does not make ablution obligatory; i.e., it is only desirable.
Allah knows best.