Hekayat 4 from Chapter 4 of Golestan of Saadi Shirazi

A respected scholar engaged in a debate with one of the heretics (may God curse them). Despite all his reasoning, he could not win the argument. He threw down his shield and walked away. Someone asked him: "With all your knowledge and wisdom, how could you not win an argument with an unbeliever?" He replied: "My knowledge is of the Quran, Hadith, and the sayings of our elders, but he neither believes in nor listens to these. What use is it for me to hear his blasphemous speech?"

For the one who is not guided by the Quran and traditions,
the best response is no response.

عالمی معتبر را مناظره افتاد با یکی از ملاحده لَعنهُم الله عَلی حِدَه و به حجت با او بس نیامد. سپر بینداخت و برگشت. کسی گفتش: تو را با چندین فضل و ادب که داری با بی‌دینی حجت نماند؟ گفت: علم من قرآن است و حدیث و گفتار مشایخ و او بدینها معتقد نیست و نمی‌شنود. مرا شنیدن کفر او به چه کار می‌آید؟

آن کس که به قرآن و خبر زو نرهی

آن است جوابش که جوابش ندهی