Abu Sa'id al-Zuraqi (Sa'd bin Umarah) (may Allah be pleased with him) narrated that a man from the tribe of Ashja' asked the Prophet (peace and blessings be upon him): "My wife is breastfeeding, and I do not want her to become pregnant; shall I practise withdrawal (azl)?" He (peace and blessings be upon him) said: "Whatever has been decreed in the womb will come to be."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5402