The Prophet (PBUH) said:
Ar-ruqa At-Tama'im and At-Tiwala are acts of polytheism Transmitted by Imam Ahmad (1/381), Abu Dawud (3883), Ibn Majja (3530) and Al-Hakim (4/418)
According to Ibn Ai-Athir, at-Tiwala is a type of sihr which makes a man love his wife. The reason why this type of sihr’s classed by the Prophet (PBUH) as an act of polytheism is because those who have it done for them believe that it has an effect and does the opposite of what Allah (SWT) has prescribed. An-Nihaya: 1/200
I would like to emphasise that the ruqya referred to in the above hadith is the one which seeks the assistance of Jinn and devils and consists of acts classed as polytheistic. However, the ruqya which is based on the Qur'an and lawful supplications of Allah is lawful, according to scholars. It is reported in Sahih Muslim that the Prophet (PBUH) was quoted as saying:
There is no harm in using ruqya as a means of treatment provided it does not consist of anything polytheistic.