Laudator Temporis Acti

Hesiod, Works and Days 100-105 (tr. Glenn W. Most):

But countless other miseries roam among mankind;
for the earth is full of evils, and the sea is full;
and some sicknesses come upon men by day, and others by night,
of their own accord, bearing evils to mortals
in silence, since the counsellor Zeus took their voice away.
Thus it is not possible in any way to evade the mind of Zeus.

ἄλλα δὲ μυρία λυγρὰ κατ' ἀνθρώπους ἀλάληται·        100
πλείη μὲν γὰρ γαῖα κακῶν, πλείη δὲ θάλασσα·
νοῦσοι δ' ἀνθρώποισιν ἐφ' ἡμέρῃ, αἳ δ' ἐπὶ νυκτὶ
αὐτόματοι φοιτῶσι κακὰ θνητοῖσι φέρουσαι
σιγῇ, ἐπεὶ φωνὴν ἐξείλετο μητίετα Ζεύς.
οὕτως οὔτι πη ἔστι Διὸς νόον ἐξαλέασθαι.        105

W.J. Verdenius on σιγῇ (line 104):

The dative has modal force, but properly denotes attending circumstances (comitativus); cf. Hom. Δ 412 σιωπῇ ἧσο, Γ 2 κλαγγῇ τ᾽ ἐνοπῇ τ᾽ ἴσαν, K.G. I, 435, Schw. II, 162, Chantr. II, 75. The meaning obviously is 'secretly' (LSJ II 2), not 'Und wenn der Mensch in seiner Qual verstummt', as is assumed by F. Dornseiff, in Heitsch, 131. For the difference between σιγάω ('be silent') and σιωπάω ('keep something quiet') cf. T. Krischer, Glotta 59 (1981), 93-107.

F.A. Paley:

The idea is, that diseases give no warning of their approach. Compare σιγῶν ὄλεθρος, Aesch. Εum. 895.

Jacob Emmeness in his edition of Vergil (Leiden, 1680), on Georgics 3.67, also adduced Seneca, Epistulae Morales 14.4 (tr. Richard M. Gummere):

But the natural evils which I have mentioned, want and sickness, steal upon us silently with no shock of terror to the eye or to the ear.

naturalia mala quae rettuli, inopia atque morbus, silentio subeunt nec oculis nec auribus quicquam terroris incutiunt.