There are three issues in this matter:

The first: That the expiation for the Zihar-performer who is capable of manumission is the emancipation of a slave, and nothing else suffices him, without any disagreement among the scholars that we know of. The basis for this is the saying of Allah, the Almighty: "And those who perform Zihar with their wives and then wish to go back on what they said, then (there is) the freeing of a slave before they touch one another" up to His saying: "But he who finds not (the means for that), then he must fast two consecutive months before they touch one another." Also, the saying of the Prophet (may Allah bless him and grant him peace) to Aws ibn al-Samit when he performed Zihar against his wife: "He shall free a slave." I said: "He does not find one." He said: "Then he shall fast." And his saying to Salamah ibn Sakhr was similar to that. So, whoever finds a slave and does not need it for his livelihood, or finds its price in excess of his needs and finds it available, nothing will suffice him but manumission; because the existence of the substituted item, when it prevents moving to the substitute, means that the capacity to afford its price prevents moving to the substitute, just as water and its price prevent moving to Tayammum.

The second issue: That nothing suffices him but the manumission of a believing slave in the expiation of Zihar and all other expiations. This is the manifest position (zahir al-madhhab) and is the opinion of al-Hasan, Malik, al-Shafi'i, Ishaq, and Abu 'Ubayd. There is a second narration from Ahmad stating that in matters other than the expiation for homicide, such as Zihar and others, the manumission of a dhimmi (non-Muslim citizen) slave suffices. This is the opinion of 'Ata', al-Nakha'i, al-Thawri, Abu Thawr, the People of Opinion (Ashab al-Ra'y), and Ibn al-Mundhir; because Allah, the Almighty, left the term 'slave' absolute in this expiation, so it is necessary that whatever is covered by the absolute term should suffice. We argue based on what Mu'awiyah ibn al-Hakam reported: "I had a slave-girl, and I came to the Prophet (may Allah bless him and grant him peace) and said: 'I am required to free a slave; shall I free her?' The Messenger of Allah (may Allah bless him and grant him peace) said to her: 'Where is Allah?' She said: 'In the heaven.' He said: 'Who am I?' She said: 'You are the Messenger of Allah.' He said