Sayyiduna Ibn Abbas (may Allah be pleased with them both) said concerning the verse "And to those with whom your oaths have made a pledge" [Surah al-Nisa': 33]: A man would make a pact with another man while there was no lineage between them, and then one of them would inherit from the other. Then the verse of Surah al-Anfal, "And those of blood relationship are more entitled to one another" [Surah al-Anfal: 75], abrogated that.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12527