Narrated Sa`id bin Jubair:
Ibn `Abbas said, "In the verse: To every one We have appointed ' (Muwaliya Muwaliya means one's) heirs (4.33).' (And regarding the verse) 'And those with whom your right hands have made a pledge.' Ibn `Abbas said, "When the emigrants came to the Prophet (ﷺ) in Medina, the emigrant would inherit the Ansari while the latter's relatives would not inherit him because of the bond of brotherhood which the Prophet established between them (i.e. the emigrants and the Ansar). When the verse: 'And to everyone We have appointed heirs' (4.33) was revealed, it canceled (the bond (the pledge) of brotherhood regarding inheritance)." Then he said, "The verse: To those also to whom your right hands have pledged, remained valid regarding cooperation and mutual advice, while the matter of inheritance was excluded and it became permissible to assign something in one's testament to the person who had the right of inheriting before.
Narrated Ibn `Abbas:
Regarding the Holy Verse:--'And to everyone, We have appointed heirs..' And:-- (4.33) 'To those also to Whom your right hands have pledged.' (4.33) When the emigrants came to Medina, the Ansar used to be the heir of the emigrants (and vice versa) instead of their own kindred by blood (Dhawl-l-arham), and that was because of the bond of brotherhood which the Prophet (ﷺ) had established between them, i.e. the Ansar and the emigrants. But when the Divine Verse:-- 'And to everyone We have appointed heirs,' (4.33) was revealed, it cancelled the other, order i.e. 'To those also, to whom Your right hands have pledged.'
Narrated Ibn `Abbas:
Regarding the Verse: "To everyone, We have appointed heirs." (4.33) 'Mawali' means heirs. And regarding:-- "And those to whom your right hands have pledged." When the Emigrants came to Medina, an Emigrant used to be the heir of an Ansari with the exclusion of the latter's relatives, and that was because of the bond of brotherhood which the Prophet (ﷺ) had established between them (i.e. the Emigrants and the Ansar). So when the Verses:-- "To everyone We have appointed heirs." was revealed, (the inheritance through bond of brotherhood) was cancelled. Ibn `Abbas then said: "And those to whom your right hands have pledged." is concerned with the covenant of helping and advising each other. So allies are no longer to be the heir of each other, but they can bequeath each other some of their property by means of a will.