To forestall any invasion of Arabia by the Byzantines, the Holy Prophet decided to undertake an expedition to Tabuk on the borders of Syria. The hot season had set in, and the season was unfavorable to the undertaking of any expedition. It was the harvesting season, and the people were generally loath to leave their homes and go to the war. In spite of these difficulties the Holy Prophet was able to raise an army of thirty thousand men. To finance the expedition, the Holy Prophet invited voluntary contributions, and the Companions subscribed liberally to the cost of the war.