The Quran

وَيَصنَعُ الفُلكَ وَكُلَّما مَرَّ عَلَيهِ مَلَأٌ مِن قَومِهِ سَخِروا مِنهُ ۚ قالَ إِن تَسخَروا مِنّا فَإِنّا نَسخَرُ مِنكُم كَما تَسخَرونَ

Muhammad Asad

And [so Noah] set himself to building the ark; and every time the great ones of his people passed byhim, they scoffed at him. [Thereupon] he said: "If you are scoffing at us - behold, we are scoffing at you [and your ignorance], just as you are scoffing at us.¹

Since it is obviously impossible to attribute to a prophet the levity of scoffing (Baghawi), the meaning of the above phrase seems to be this: "If you consider us ignorant because of what we believe and are doing, we consider you ignorant because of your refusal to acknowledge the truth and your readiness to expose yourselves to God's punishment" (Zamakhshari and, in a shorter form, Baghawi). Hence my interpolation of the words "and your ignorance".