(8) باب التَّسْمِيَةِ عَلَى كُلِّ حَالٍ وَعِنْدَ الْوِقَاعِ
Narrated Ibn `Abbas:
The Prophet (ﷺ) said, "If anyone of you on having sexual relations with his wife said (and he must say it before starting) 'In the name of Allah. O Allah! Protect us from Satan and also protect what you bestow upon us (i.e. the coming offspring) from Satan, and if it is destined that they should have a child then, Satan will never be able to harm that offspring."
Reference: Sahih al-Bukhari 141
In-book reference: Book 4, Hadith 7
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 1, Book 4, Hadith 143