Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) was asked about 'azl, and he (peace and blessings be upon him) said: "Does a child come from all of the fluid (i.e., semen)? When Allah Almighty wills to create someone, there is none who can prevent it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14311