The Prophet (peace and blessings be upon him) said: "There are three people whom it is a right upon Allah to help: the one who strives in jihad in the path of Allah, the one who marries intending to keep away from evil, and the mukatab who intends to pay (for his freedom)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13456