What is the way to advise a relative who is convinced of the Ahmadiyya religion and is trying to convince others of it, knowing that he believes himself to be in the right, using verses such as "Verily! You guide not whom you like, but Allah guides whom He wills"?

It appears that the questioner, by "Ahmadiyya," means the Qadianis, who are a disbelieving, renegade sect, or the Rifa'iyya. Their doctrines have already been explained.

The questioner should learn what protects their religion, focusing on creed. Then, they should become acquainted with the misguided doctrines of the sect in order to invite their relative with knowledge and insight. They should be firmly grounded in knowledge and secure from temptation before confronting people of misguidance.

If they undertake to invite their relative, they must explain that the religion with Allah is Islam, and that Muhammad, peace and blessings be upon him, is the Seal of the Prophets, and that whoever claims prophethood after him is a disbeliever.

They should also frequently supplicate for his guidance, and be gentle and patient in their invitation, and not despair of him, for perhaps Allah will guide him through their hands.