Hadith 10:1501
Abu Bakr narrated to us, he said: Abbad bin al-Awwam narrated to us, from Juwaybir, from al-Dahhak, from Abdullah, who said: If he divorces secretly and takes her back secretly, that is a return (raj'ah). If he has intercourse, there is no harm. But if he divorced with the intention (of it being known) and took her back, then let him call witnesses to his return.
حدثنا أبو بكر قال نا عباد بن العوام عن جويبر عن الضحاك عن عبد الله قال إذا طلق سرا راجع سرا ذلك رجعة فإن واقع فلا بأس وإن طلق على نيته وراجع فليشهد على رجعته