Kohelet Rabbah 2.6

עָשִׂיתִי לִי בְּרֵכוֹת מָיִם, פּוֹסְקִינוֹס, לְהַשְׁקוֹת מֵהֶם יַעַר צוֹמֵחַ עֵצִים, זוֹ אֶרֶץ יִשְׂרָאֵל, שֶׁנֶּאֱמַר (מלכים א י, יז): וַיִּתְּנֵם הַמֶּלֶךְ בְּבֵית יַעַר הַלְּבָנוֹן.

“I made myself pools of water to irrigate from them a forest which grows trees” (Ecclesiastes 2:6). “I made myself pools of water” – an irrigation system; “to irrigate from them a forest which grows trees” – this is the Land of Israel, as it is stated: “[Three hundred shields of gold…] The king placed them in the house of the forest of Lebanon” (II Chronicles 9:16).