The signing of the partnership was part of activities lined up for UFC Freedom 250.
The Last Stylebender dominated the three rounds out of the previous four rounds, before blowing it away with just two minutes remaining.
The Nigerian was declared winner by all three judges based on huge margins from four and five rounds.
Chidi Njokuani put up a dominant display to TKO Mario Sousa in Round 3.
It was another impressive victory for Islam who many believe is the champion in waiting.
The match, which is the major live sports event where full crowds are allowed in Nevada, is the third meeting between the fighters.
Nigerian-born Dan Ige suffered a setback in his bid to rise through the ranks in UFC.
