I have always said, "Our hope and prayer is..." but was recently corrected by my husband and told that the correct grammar would be, "Our hope and prayer are...". Which one is correct?
This is mere hypercorrection. It is an error to believe that and automatically creates two different things. It does not always do so.
Because hope and prayer is one thing, it takes a singular verb: “My hope and prayer is that he should return unharmed.”
It’s like saying “My lord and husband is away.” That’s just one person. Only if it referred to two different people would it take a plural verb.
Somewhat differently, you would say that “Ham and cheese is my favorite sandwich.” This time although ham and cheese are two different things, ham and cheese is one kind of sandwich and so they are taken together as a single thing.