Sayyiduna al-Hajjaj bin Malik al-Aslami (may Allah be pleased with him) said to the Messenger of Allah (peace and blessings be upon him): O Messenger of Allah, What is appropriate to give to discharge the obligation owed for suckling? He (peace and blessings be upon him) said: "A male slave or a female slave."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3196