Reference for Shevuot 52:3
כמאן כמונבז דאמר שגגת קרבן שמה שגגה
Samuel said: If he decided in his mind, he must utter it with his lips, for it is said: to utter with the lips. An objection was raised: with the lips, but not in the mind. If he decided in his mind, how do we know [that he is liable]? Because it is said: whatsoever it be that a man shall utter clearly with an oath. This itself is contradictory! You say, with the lips, but not in the mind; and then you say, if he decided in his mind, how do we know [that he is liable]? - R. Shesheth said: This is no question; thus he means: with the lips, but not if he decided in his mind to utter it with his lips, and did not utter it. If he decided in his mind, simply, how do we know [that he is liable]? Because it is said: whatsoever it be that a man shall utter clearly. But against Samuel the question remains! - R. Shesheth said: Answer it thus: with the lips, but not if he decided in his mind to utter 'wheat bread', and he uttered 'barley bread'. If he decided in his mind to utter 'wheat bread', and he uttered 'bread' simply, how do we know [that he is liable]? Because it is said: whatsoever it be that a man shall utter clearly. <br>