The scholar saying "I do not know" when asked about a matter he does not know the answer to

The Shaykh : And it is not difficult for you that one who is greater than us in knowledge, when asked about a matter, says "I do not know," for half of knowledge is "I do not know." It is established from some of the imams of the Salaf, and I think it was Imam Malik, that a man from Khurasan came to him with a list longer than this one, containing one hundred questions from the people of Khurasan. They sent these questions with this man, saying, "Ask Imam Malik, the imam of the city of migration, and get the answers for us from him." So he took the paper, studied it, and gave the answer to only three out of the one hundred questions. The messenger was astonished and said, "You are the imam of the city of migration, and we sent you specifically with one hundred questions, and you give me only three?" He said to him, "Go back and tell them that Imam Malik does not know the answer to these questions except for these three." This is the way the people of knowledge are; they do not say what they do not know, because Allah (Mighty and Majestic) forbade the Muslim from saying what he does not know. Therefore, we always say in our supplications, "My Lord, increase me in knowledge." Why? Because Allah said: , and this is what we have not been given until now. My answer is "I do not know," "I do not know." Yes.
The student : May Allah reward you with good.

The Shaykh : And beware of that.
The student : A third question, or the last one.