[4:25] Those among you who cannot afford to marry free believing women, may marry believing slave women. GOD knows best about your belief, and you are equal to one another, as far as belief is concerned. You shall obtain permission from their guardians before you marry them, and pay them their due dowry equitably. They shall maintain moral behavior, by not committing adultery, or having secret lovers. Once they are freed through marriage, if they commit adultery, their punishment shall be half of that for the free women.* Marrying a slave shall be a last resort for those unable to wait. To be patient is better for you. GOD is Forgiver, Most Merciful.

*4:25 This law proves that the punishment for adultery could not possibly be stoning to death as stated in the laws of corrupted Muslims (see 24:2).

Adultery
[24:2] The adulteress and the adulterer you shall whip each of them a hundred lashes. Do not be swayed by pity from carrying out GOD's law, if you truly believe in GOD and the Last Day. And let a group of believers witness their penalty.*

*24:2 Social pressure, i.e., public witnessing of the penalty, is the basic punishment (see also 5:38). The lashes shall be symbolic, not severe.