Ubaydullah narrates from Nafi' that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) gave his wife Safiyyah bint Abi Ubayd one or two divorces, so he used to go to her (only) after seeking permission; and when he took her back and made witnesses to it, he would then go to her without permission.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرجعة / 15188