A solemn declaration is a serious statement made by someone that holds legal significance. It is a formal and solemn promise or affirmation about something important, often given under oath. Full definition
The only thing is that the wise or solemn declarations of the world about God can disturb Israel, the church, and the Christian. (religion-online.org)
(ii) together with members of her family enter into solemn declarations on the Koran before an Imam in the Regent's Park Mosque or head of The Muslim College, granting the safe return of the child; (newlawjournal.co.uk)
When he makes a solemn declaration of a papal definition, he is preserved from the possibility of error. (religion.blogs.cnn.com)