In the first place, we would like to stress that when a man wants to have intercourse with his wife, he should say (as mentioned in the Prophetic hadith): “Bismillah, Allahumma janniba ash-shaytan wa jannib ash-shaytan ma razqtana (In the name of Allah. O Allah! Keep us away from Satan and keep Satan away from what You bestow on us (our children)).” The Messenger of Allah (peace and blessings be upon him) said: “If Allah decrees that they should have a child, Satan will never harm him.” (Al-Bukhari).
Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: “You can recite the regular waza’if (spiritual du`a’s and dhikr) including Al-Fatihah, ayat Al-Kursi, surat Al-Ikhlas, surat Al-Falaq, and surat An-Nas. You can also readsurat Maryam as some scholars have suggested. As well as this, you can always make dhikr by reciting formulas such as subhana Allah, al-hamdu lillah, la ilaha illa Allah, Allahu akbar, wa la hawla wa la quwwata illa bi Allah (Glory be to Allah, all praise be to Allah, there is no god but Allah. Allah is the most Great. There is no strength or power except by the will of Allah), etc.
As Imam Ibn al-Qayyim said: Consistency in dhikr renders all difficult tasks easy. The Prophet (peace and blessings be upon him) said, “Whoever clings to istighfar (seeking Allah’s forgiveness), Allah will appoint for him/her a way out of all troubles, and will provide for him/her in ways he/she could never foresee in ordinary times!”
So cling to dhikr and istighfar and Allah will surely make things easy for you.”