"My wife is breast-feeding and I do not want her to get pregnant." The Prophet said: "What has been decreed in the womb will come to be."
Sunan an-Nasa'i Book 26, Hadith 133
← Previous Hadith "Why do you do that?" We said: "A man may have a wife, and he has intercourse with her, but he does not want her to get pregnant, or he may have a concubine, and he has intercourse with her, but he does not want her to get pregnant." He said: "It does not make any difference if you do that, for it is the matter of Al-Qadr."

Sunan an-Nasa'i Book 26, Hadith 132 Next Hadith → "I said: 'O Messenger of Allah, how can I pay back the dues of the one who breast-fed me?' He said: 'By giving a male or female slave.'"

Sunan an-Nasa'i Book 26, Hadith 134