Ibn Ishaq writes that during the siege, the Qurayza readmitted Huyayy ibn Akhtab, the chief of the Banu Nadir whom Muhammad had exiled and who had instigated the alliance of his tribe with the besieging Quraysh and Ghatafan tribes. According to Ibn Ishaq, Huyayy persuaded the Qurayza chief Ka'b ibn Asad to help the Meccans conquer Medina. Ka'b was, according to Al-Waqidi's account, initially reluctant to break the contract and argued that Muhammad never broke any contract with them or exposed them to any shame, but decided to support the Meccans after Huyayy had promised to join the Qurayza in Medina if the besieging army would return to Mecca without having killed Muhammad. Ibn Kathir and al-Waqidi report that Huyayy tore into pieces the agreement between Ka'b and Muhammad.