This is a scholastic maxim, that can be translated : "abstraction does not falsify" (lit.: there is no lie of/from those who abstract) and is traditionally referred to Aristote (II Physic., 193b 35).
Scotus (in II Physic., Expositio 20 textus 1
says: "Et si
aliquis dicat, quod Mathematici tunc faciunt mendacium: quia considerant ista,
quasi essent abstracta a motu, et materia; quae tamen sunt coniuncta materiae.
Respondet, quod non faciunt mendacium: quia Mathematicus non considerat,
utrum id, de quo demonstrat suas passiones, sit coniunctum materiae, vel
abstractum a materia."
[And if someone says that mathematicians tell lies because they consider these things as if they were abstracted from move and matter, whereas they are conjoined with matter; he responds that they do not tell lies, because mathematician doesn't consider whether it, about which he demonstrates its passions (= accidents), is conjoined with matter or abstracted from matter.]
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