What is the guideline for mentioning the source of religious information for someone who delivers the Friday sermon and uses books and sayings of scholars, then summarizes and rephrases them in their own way? Is it obligatory for him to mention that he summarized it or took it from certain sources?

Summarizing lessons and sermons is permissible, but if the summary has a source, that source must be indicated for academic integrity, such as quoting from a book or a website. Sources and references should be mentioned when publishing, in adherence to academic integrity and intellectual property rights. Permission from authors is not required for quoting; rather, statements are attributed to their originators. If a preacher mentions a statement by someone else and forgets its source, he should indicate it in a way that makes clear it is not his own statement.