Source and decoding - Bava Batra 14b
תָּנוּ רַבָּנַן, סִדְרָן שֶׁל נְבִיאִים: יְהוֹשֻׁעַ וְשׁוֹפְטִים, שְׁמוּאֵל וּמְלָכִים, יִרְמְיָה וִיחֶזְקֵאל, יְשַׁעְיָה וּשְׁנֵים עָשָׂר. מִכְּדֵי הוֹשֵׁעַ קָדֵים; דִּכְתִיב:
The Sages taught: the order of the Prophets - Joshua and Judges, Samuel and Kings, Jeremiah and Ezekiel, Isaiah and the Twelve.
The Sages taught: the order of the Prophets - Joshua and Judges, Samuel and Kings, Jeremiah and Ezekiel, Isaiah and the Twelve. The Gemara objects: Hosea came first, as it says "the beginning of God's word through Hosea"! It explains he was first of four prophets of that period.