וַתָּבֹ֨א אֵלָ֤יו הַיּוֹנָה֙ לְעֵ֣ת עֶ֔רֶב וְהִנֵּ֥ה עֲלֵה־זַ֖יִת טָרָ֣ף בְּפִ֑יהָ וַיֵּ֣דַע נֹ֔חַ כִּי־קַ֥לּוּ הַמַּ֖יִם מֵעַ֥ל הָאָֽרֶץ׃
And the dove came in to him at eventide; and lo in her mouth an olive-leaf freshly plucked; so Noah knew that the waters were abated from off the earth.
Read kabbalistic (mystical) interpretation of Genesis 8:11: and classical mystical sources.