Luke 20:7

And they answered, that they could not tell whence it was.

The answer was given during Jesus' final visit to the temple, when as Israel's King He confronted the corrupt priesthood and set evidence of His divine mission before an unbelieving people, though He knew His effort to reform them would be in vain. It was His reply to the counter-question whether John's baptism was from heaven or from human authority. The priests and rulers refused a direct answer because either course condemned them, for to deny John's divine mission would anger the people who held John to be a prophet, while to acknowledge it would force them to explain why they had rejected his testimony concerning Jesus. Their claim that they could not tell was mere pretense covering unwillingness to receive the truth, and it was cowardly, dishonest and indecisive. By that evasion they lost the respect of the people who witnessed it. Because of that dishonest evasion Jesus withheld from them the statement by what authority He acted.