affirmation

Short definition from Wiktionary

Noun

1. 1
   That which is affirmed; a declaration that something is true.
2. 2
   A solemn pledge (to tell the truth, to bear allegiance, etc.), legally equivalent to an oath, taken by people who are forbidden to take a religious oath (such as Quakers) or otherwise prefer not to do so.
3. 3
   A form of self-forced meditation or repetition; autosuggestion.