וְהַיָּמִ֗ים אֲשֶׁר֩ מָלַ֨ךְ שְׁלֹמֹ֤ה בִירוּשָׁלִַ֙ם֙ עַל־כָּל־יִשְׂרָאֵ֔ל אַרְבָּעִ֖ים שָׁנָֽה׃
And the time that Solomon reigned in Jerusalem over all Israel was forty years.
Read midrashic interpretation of I Kings 11:42: and classical rabbinic exegesis.