Is it permissible to have intercourse with one's wife after the cessation of postpartum bleeding but before she performs ghusl, and could this result in pregnancy?

It is not permissible to have intercourse with one's wife after the cessation of postpartum bleeding (nifas) and before she performs ghusl (ritual bath). No expiation is obligatory for the one who does so, but he must seek forgiveness from Allah Almighty and repent to Him, regardless of whether a pregnancy resulted from it or not.