Musnad Abu Ya'la al-Mawsili 160:140

Abu Bakr ibn Abi Shaybah narrated to us, Abu Khalid narrated to us, from Ibn ‘Ajlan, from Sa’id, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Three are all entitled to the help of Allah: the warrior in the way of Allah, the slave who has a contract of manumission (mukātab) who desires to pay off [his debt], and the one who marries desiring chastity."