It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When any of you goes to his wife, let him not fail to say: 'In the name of Allah. O Allah, keep me and what You have granted me away from Satan the accursed.' Then, if it is decreed that a child be born to the two of them, Satan will never harm it."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7810