λευκὸν ἧμαρ νυκτὸς ἐκ μελαγχίμου

From LSJ

ψυχῆς πείρατα ἰὼν οὐκ ἂν ἐξεύροιο πᾶσαν ἐπιπορευόμενος ὁδόν· οὕτω βαθὺν λόγον ἔχει → one would never discover the limits of soul, should one traverse every road—so deep a measure does it possess

Source