Yahya said: I said to Qasim, "It is very hard for me that someone asks you a question and you express ignorance about it, even though your father was the Imam of the time." He replied, "It is even harder and more severe (a harsher matter) with Allah and with those who have understanding about Allah, that I should give a fatwa without knowledge or narrate something from an unreliable narrator."
Hadith Takhrijاس روایت کی سند ضعیف ہے۔ محمد بن کثیر کی وجہ سے، لیکن معنی صحیح ہے ۔ دیکھئے: [مقدمة صحيح مسلم 16/1] ، [معرفة السنن والآثار 141/1]
Brief Explanation
(Commentary on Hadiths 113 to 115)
From this, it is understood that: they did not consider it shameful to say «لا ادري» or «لا اعلم», that is, "I do not know about this," in response to a question, even though they too were great scholars and jurists of their time. This demonstrates their virtue.
Additionally, the dislike of narrating hadith from an unreliable (ghayr thiqah) narrator is also understood from this.