It is narrated from Sayyiduna Malik bin al-Huwayrith (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When Allah, the Blessed and Exalted, intends to create a soul and the man has intercourse with his wife, his fluid (semen) spreads into every vein and sinew of the woman; then when the seventh day comes, Allah Almighty brings forth for it (the child) every vein between it and Sayyiduna Adam (peace be upon him)." Then he (peace and blessings be upon him) recited this verse: "In whatever form He willed, He has put you together."
Imam al-Tabarani (may Allah have mercy on him) said: "This hadith is not narrated from Sayyiduna Malik (may Allah be pleased with him) except with this chain, and Unays is alone in narrating it."
Hadith Referenceالمعجم الأوسط / باب الألف / 1613
Hadith Takhrij«أخرجه الطبراني فى «الكبير» برقم: 644، والطبراني فى «الصغير» برقم: 106»