Aristophanes, Birds 1417 (web address 1), with scholion. (The preceding line, 1416, has mentioned a cloak.) The present headword phrase comes from those scholia, but appears as proverbial in its own right in Appendix Proverbiorum 2.3.
The proverb "One swallow does not make a spring" (we would say "summer"), Cratinus fr.33 Kock, is quoted by Aristotle at Nichomachean Ethics 1098a16 (web address 2): cf. mu 1030.