It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that, regarding the saying of Allah Almighty: "And to those with whom your oaths have made a pledge, give them their share" [Surah al-Nisa': 33]: When the Muhajirun came to Madinah, they were made heirs of the Ansar, to the exclusion of their own relatives, because of the brotherhood that the Messenger of Allah (peace and blessings be upon him) had established between them. When the verse "And for each We have appointed heirs of what parents and near relatives leave" [Surah al-Nisa': 33] was revealed, it abrogated the first verse, and "And to those with whom your oaths have made a pledge, give them their share" [Surah al-Nisa': 33] means "help and sincere counsel".
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12525