Praise be to Allaah.
This is not necessarily the case, but it could happen. Some people are tested by means of someone else putting a magic spell on them which prevents them from having intercourse with their wives. Allaah says (interpretation of the meaning):
“And from these (angels) people learn that by which they cause separation between man and his wife, but they could not thus harm anyone except by Allaah’s Leave [al-Baqarah 2:102]
But if a person uses the prayers for refuge prescribed in Islam, Allaah will be sufficient for him against the evil of the magicians and others, and Allaah will take that (magic) away if it is present. So he has to read Aayat al-Kursi over himself, and al-Faatihah, and the verses which speak of sihr (magic), and “Qul Huwa Allaahu Ahad” and the Mi’wadhatayn, and it will go away by Allaah’s Leave. This has been tried a great deal. A good qaari’ (reader) from among the good and righteous people from whom one hopes for good may also recite for him. The reader may recite into water which the man may then drink from or wash with, and the harm will go away from him, or the reader may recite over him and blow onto him, and Allaah will cure him of that. All of these are means of keeping safe and sound.