According to Numbers 11: 16 (NASB), God told Moses to bring 70 elders to the tent of meeting. (This was after the Hebrews complained that they were tired of eating manna and wanted meat like they had eaten in Egypt. Overwhelmed and exasperated, Moses called upon the LORD. (I recommend reading the whole chapter to put these verses in context. Read all of I Corinthians 14 also.)
Then the LORD came down in the cloud and spoke to him; and He took of the Spirit who was upon him and placed Him upon the seventy elders. And when the Spirit rested upon them, they prophesied. But they did not do it again. But two men had remained in the camp; the name of one was Eldad and the name of the other Medad. And the Spirit rested upon them . . . and they prophesied in the camp” (Numbers 11: 25, 26).
Then Joshua the son of Nun . . . said, “Moses, my lord restrain them.” But Moses said to him, “Are you jealous for my sake? Would that all the LORD’s people were prophets, that the LORD would put His Spirit upon them!” (Numbers 11: 28, 29)
Compare the verses above in Numbers with the verses below in I Corinthians:
“For you all can prophesy one by one, so that all may learn and all may be exhorted; Therefore, my brethren, desire earnestly to prophesy” (I Corinthians 14: 31, 39a).
Whenever Paul referred to the scriptures, he was referring to the Old Testament (a.k.a the Tanakh) because the New Testament had not been written–nor would it be canonized for another 300 years. The New Testament is a Jewish document, that ties in perfectly with the Tanakh.