высосать из пальца

Etymology
lit. 'to suck out of one's finger'. Compare 🇨🇬, 🇨🇬, 🇨🇬, 🇨🇬.

Verb

 * 1)  to think of something, to make up, to make up out of thin air, to invent, to pull out of one's ass fabricate a claim with no factual basis or evidence