to the best of (something)
To the absolute or utmost extent of something. To the best of my knowledge, our company has never signed any sort of exclusivity deal regarding our intellectual property. The team played to the best of their ability, but it wasn't enough to overcome the returning champions' stellar defense.
to the best of
To the utmost extent of, especially of one's ability, knowledge, or power. For example, I'm sure he'll do it to the best of his ability, or To the best of my knowledge, they arrive tomorrow. [c. 1500]