Before he atoned, he said: "One expiation."(1)

This is a good and strange hadith.

The practice according to most of the people of knowledge is in accordance with this, and it is the saying of Sufyan, Malik, al-Shafi'i, Ahmad, and Ishaq.

And some of them said: If he has intercourse with her before he atones, then he owes two expiations, and this is the saying of 'Abd al-Rahman ibn Mahdi.

1238 - Abu 'Ammar al-Husayn ibn Hurayth narrated to us, he said: al-Fadl ibn Musa narrated to us, from Ma'mar, from al-Hakam ibn Aban, from 'Ikrimah, from Ibn 'Abbas: That a man came to the Prophet, peace and blessings be upon him, who had pronounced zihar upon his wife and then had intercourse with her. He said: "O Messenger of Allah, I pronounced zihar upon my wife and then had intercourse with her before I atoned." He said: "And what compelled you to do that, may Allah have mercy on you?" He said: "I saw her anklet in the light of the moon." He said: "Then do not approach her until you do what Allah has commanded you."(2)

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(1) Authentic by its chains and its witness, and it was transmitted in full and abbreviated form by Abu Dawud (2213) and (2217), and Ibn Majah (2062) and (2065), and it is in al-Musnad (16419), and it will come in full form under number (1239) and (3584).
And the hadith of Ibn 'Abbas that follows after this bears witness to it.
(2) Authentic by its chains and by what precedes it. Al-Hakam ibn Aban was declared trustworthy by Ibn Ma'in, al-Nasa'i, Ahmad, al-'Ijli, Sufyan ibn 'Uyaynah, Ibn Numayr, Ibn al-Madini, and others, and the rest of its narrators are trustworthy, and it has been declared defective due to interruption (irsal).
And it was transmitted by Abu Dawud (2223), Ibn Majah (2065), and al-Nasa'i 6/167.