If she commits adultery, does he re-enslave her or not?

Ibrahim (may Allah have mercy on him) said: If an umm walad commits an indecent act, she will not return to slavery; rather, she remains in her existing state. When her master dies, she will be counted as free.

Al-Hasan and Ibrahim (may Allah have mercy on them) did not consider the sale of an umm walad to be proper, even if she commits an indecent act.

And Ibn Sirin held that she may be sold.

Umar bin Abd al-Aziz wrote: An umm walad is free, even if she commits an indecent act.

Al-Sha'bi (may Allah have mercy on him) said: No new act (occurrence) will bring an umm walad back into slavery.

Umar bin Abd al-Aziz said: Even if an umm walad commits an indecent act, she will still not be sold.

Salim bin Abdullah was asked: If an umm walad commits an indecent act, may I sell her? He (may Allah have mercy on him) said: No. Her wrongdoing is upon her own soul (its burden is on her alone), and she is free.

Sayyiduna Umar (may Allah be pleased with him) said concerning an umm walad: If she remains chaste and Muslim, she is free. And if she does wrong, becomes a disbeliever and commits fornication, she returns to slavery.