Ikrimah narrates from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) returned his daughter Sayyidah Zaynab (may Allah be pleased with her) to Abu al-As on the basis of the first marriage after six years. In the narration of Yunus: on the basis of the first marriage; nothing new (no new marriage contract) was done after six years. This is because, with Sayyidah Zaynab's (may Allah be pleased with her) acceptance of Islam, then her emigration to Madinah, and Abu al-As's refusal of Islam, her marriage did not become dependent on the end of the waiting period, until, after the Truce of Hudaybiyyah, the verse was revealed making Muslim women unlawful for the polytheists: "They are not lawful for them, nor are they lawful for them." [Surah al-Mumtahanah: 10] After this verse was revealed, her marriage became dependent on the end of her waiting period. Only a short time had passed when Abu Basir and others took Abu al-As captive and sent him to Madinah, and Sayyidah Zaynab (may Allah be pleased with her) gave him protection. Then he returned to Makkah, gave back all the deposits he held, and declared his Islam. So between her marriage becoming dependent on the end of the waiting period and his acceptance of Islam there was only a short interval.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14068