2 Timothy 2:15:

Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.

See also:

Objection: So-and-So Who Preaches Healing Got His Doctrine from So-and-So, Who Got His Doctrine from So-and-So, Who Was into Cult Theology
Objection: You Can’t Build Up Faith Yourself Because It Is a Gift from God