It is narrated from Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) that he said: "When the Prophet (peace and blessings be upon him) and his Companions (may Allah be pleased with them) came to Madinah and the Ansar gave them shelter, all the Arabs became like a single bow against them (that is, they united in enmity); then this verse was revealed: 'He will surely make them successors in the land' to the end of the verse."
This hadith is not narrated from Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him) except with this chain, and Ahmad bin Sa'id al-Darimi (may Allah have mercy on him) is alone in narrating it.
Hadith Referenceالمعجم الأوسط / باب الميم / 7029
Hadith Takhrij«أخرجه الضياء المقدسي فى «الأحاديث المختارة» برقم: 1145، 1146، والحاكم فى «المستدرك» برقم: 3533»