Surah 4. An-Nisaa', Ayah 33

I.e., wives and husbands (Abu Muslim, as quoted by Razi).

 This pledge was a common practice before Islam between friends and allies—taking oaths to inherit each other. This practice came to an end with the revelation of verse 8:75 of the Quran. Although friends and allies do not have a share in inheritance anymore, they still can get some of the estate through bequest.

Mawali, plural of Maula; from the root wala, to be near in place or relationship, to follow, Maula may therefore mean: (1) nearly related, (2) heir, (3) sharer or partner; these three meanings are implied here; (4) neighbour, or friend, or protector, or client (xliv. 44); (5) lord or master (xvi. 76).

When the emigration took place from Makkah to Madinah, bonds and links of brotherhood were established between the Emigrants and the Helpers, and they shared in each other's inheritance. Later, when the Community was solidly established, and relations with those left behind in Makkah were resumed, the rights of blood-relations in Makkah, and the Helper-brethren in Madinah were both safeguarded. This is the particular meaning. The more general meaning is similar; respect your ties of blood, of neighbourhood, and of friendly compacts and understandings. Be just to all.