Which scripture was Paul quoting in 1 Corinthians 15:45? Paul says while teaching about resurrection of the dead  and resurrected body:  


  1 Corinthians 15:45 (NET)
  So also it is written, “The first man, Adam, became a living person”; the last Adam became a life-giving spirit.  


It is clear reference from some scripture to Jesus which Paul is referring. Which book or writings Paul was referring here?
The phrase is a direct quotation from Genesis 2.7. There is some difference in the wording in most modern bibles. This is because Paul was quoting from the Greek text of the Old Testament, known as the Septuagint or LXX, whereas our modern bibles are translated from the Hebrew text from which the Greek was originally translated.

The LXX text of Genesis 2.7:


  ἐγένετο ὁ ἄνθρωπος εἰς ψυχὴν ζῶσαν


The Greek text of 1 Corinthians 15.45:


  ἐγένετο ὁ πρωτος ανθρωπος αδαμ εἰς ψυχὴν ζῶσαν


So Paul uses the exact same words, but adds the words in bold (πρωτος meaning "first" and "αδαμ" meaning "Adam") to add clarity to the meaning.

If we followed the conventions of modern writing, we'd add quotation marks and square brackets to indicate a direct quotation and an interpolation, but obviously that wasn't the custom in the ancient world.