Commentary Par XVII 118

Beginning with Scartazzini (DDP Scartazzini.Par.XVII.118) the Aristotelian provenance of this gesture has been amply noted (the beginning of the Ethics [I.4]): 'For friends and truth are both dear to us, but it is a sacred duty to prefer the truth.'  Dante himself has quoted or referred to this dictum on at least three occasions (Conv.IV.viii.13; Mon.III.i.3; Epist.XI.11).  Cf. also the frequently cited Aristotelian tag, 'Assuredly, I am Plato's friend, but I am still more a friend to truth.'