From Tripoli the Muslim forces marched to Subetula the capital of Gregory. All told the Muslim forces numbered 30,000. The forces of Gregory were twice the strength of the Muslim force. The two forces clashed outside Subetula. The war dragged on for several days without leading to any tangible result.

Gregory had a daughter Sabiyya renowned for her beauty and bravery. Gregory announced that whosoever killed Abdullah b Sa'ad, the Commander of the Muslim forces, would be married to Sabiyya as his reward, and would be declared as the heir to the Crown. This declaration caused some anxiety among the Muslims and Abdullah b Sa'ad fearing for his life remained confined to his camp. That led to a state of stalemate in the fortunes of the war.

One day Abdullah b Zubair saw Abdullah b Sa'ad in his camp, and advised him to make a counter declaration to the effect that whosoever killed Gregory would be married to Sabiyya the daughter of Gregory. This counter declaration became a cause of great concern in the camp of Gregory.

A few days passed, and still the stalemate continued. Then Abdullah b Zubair with the help of a Berber came to know of a secret way to the camp of Gregory. He decided to take the bold step of penetrating to the camp of Gregory and killing him. He ordered a regiment of the cavalry to follow him, and remain at striking distance. According to plan, Abdullah b Zubair managed to reach the camp of Gregory, and before any one could realize what had happened, he severed the head of Gregory when the forces of Gregory rushed to get hold of Abdullah, the Muslims cavalry rushed at the force of Gregory and made minced meat out of them. The battle of Subetula was won by the Muslims.