Trung Bộ Kinh (Majjhima Nikaya) 5:113
SUJATOYassa ca pana me bhāsitassa atthaṁ na ājāneyyātha, ahaṁ vo tattha paṭipucchitabbo, ye vā panāssu viyattā bhikkhū.
But if I’ve said anything that you don’t understand, you should ask me about it, or some competent mendicants.