Azrah narrates from Sa'id bin Jubayr (may Allah have mercy on him) that Mus'ab did not separate the two who performed li'an. Sa'id (may Allah have mercy on him) says: This was mentioned to Sayyiduna Abdullah bin Umar (may Allah be pleased with them both), and he said: "The Messenger of Allah (peace and blessings be upon him) separated the two who performed li'an."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب اللعان / 15327