What is the expiation for indecency with someone other than one's wife?

"Al-rafath" (indecent talk/sexual intercourse) refers to sexual intercourse and its preliminaries. It is forbidden with anyone other than one's wife and has no expiation except repentance. Sexual intercourse with anyone other than one's wife is called zina (fornication/adultery), and it has a prescribed punishment in this world: flogging for the unmarried and stoning for the married, based on the Almighty's saying: "The fornicating woman and the fornicating man, lash each one of them with a hundred lashes," and the Prophet's (peace be upon him) saying: "For the unmarried man with the unmarried woman, a hundred lashes and banishment for a year; and for the married man with the married woman, a hundred lashes and stoning." If the perpetrator is fasting or performing Hajj, zina invalidates the fast and Hajj, necessitates expiation for the fasting person, and necessitates a sacrificial animal for the pilgrim if intercourse occurs before the first stage of exiting ihram. These expiations are obligatory due to sexual intercourse with one's wife and with others.