You divorced (in a manner that is) against the Sunnah and took back (in a manner that is) against the Sunnah. Call someone to bear witness to her divorce and to her reunion, and do not do that again

In this Hadīth, ‘Imrān ibn Husayn (may Allah be pleased with him) was asked about a man who divorced his wife and then had intercourse with her after he took her back in marriage, but without calling anybody to witness either divorce or reunion. ‘Imrān (may Allah be pleased with him) answered that such a husband has violated the Sunnah in both cases as he has not brought witnesses to the divorce or to the reunion. He ordered him to bring witnesses for the divorce and the reunion and to avoid doing so again.