gutta cavat lapidem

Latin

Literally, “the water drop bores through the rock”. Perhaps a loose calque of Ancient Greek πέτρην κοιλαίνει ῥανὶς ὕδατος ἐνδελεχείῃ (pétrēn koilaínei rhanìs húdatos endelekheíēi), a verse by fifth-century BCE poet Choerilus of Samos.

Though the exact quoted words are first found in Ovid, the idea appears twice in Lucretius already:

c. 99 BCE – 55 BCE, Lucretius, De rerum natura 4.1286–1287:

nonne vides etiam guttas in saxa cadentis / umoris longo in spatio pertundere saxa?

Don't you see, besides, how drops of water falling down against the stones at last bore through the stones?

(idiomatic) little strokes fell great oaks, slow and steady wins the race
- 12–13 BCE, Ovid, Letters from the Black Sea 4.10.5:
  gutta cavat lapidem, consumitur anulus usu
  the drop bores the rock, the ring is worn out by use

gutta cavat lapidem in Treccani.it – Vocabolario Treccani on line, Istituto dell'Enciclopedia Italiana