Sahih Muslim | Book 33 | Hadith Number 6396

Narrated by Hadhaifa b. Usaid Ghifari
Hadhaifa b. Usaid Ghifari, a Companion of Allah's Messenger (may peace be upon him), reported it directly from Allah's Messenger (may peace upon him).as he said: There is an angel who looks after the womb when Allah decides to create anything after more than forty nights are over; the rest of the hadith is the same.