Reference: Siyar A’laam an-Nubalaa – Volume 12, Page 63
Suhnoon was asked whether it is possible for a scholar to say ‘I do not know’ in response to a matter he knows about? He replied:
As for that which [he knows] is affirmed in the Book and the Sunnah, then no [he cannot say ‘I do not know’]. As for that [matter] which is open to opinion, then yes it is possible [to say ‘I do not know’]. That is because he does not know [for sure] whether he is right or wrong[1].
Translator’s note:
[1] The Prophet ﷺ said:
«If a judge passes a ruling [to the best of his ability and knowledge] and gets it right, he will have two rewards. If he passes a ruling [to the best of his ability and knowledge] but gets it wrong, he will have one reward.» – transmitted by al-Bukhaaree and Muslim.