All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
A Muslim should not doubt too much, because those who doubt too much eventually doubt every person. However, it is permissible for a person to protect himself with the legislated mention of Allaah; in this regard please refer to Fatwa 88705.
As regards slaughtering, if it is in order to get closer to Allaah and seek His Pleasure, then this is something praised and its doer is rewarded. However, if the slaughtering is for other than Allaah, then it is an act of Shirk [associating partners to Allaah] and it is not permissible to do it in order to repel evil eye or anything else.
Allaah Knows best.