Originally Answered: Jesus often quoted scripture, but what exactly was considered scripture in His day?
All of the quotes that Jesus made come from a Greek translation of the Torah called the Septaigant. In included all the books of the Hebrew scriptures (which are the same as the 39 books of the Protestant Old Testament) plus nine small books or additions to Daniel and Esther that are only found in this Greek translation and included in the Catholic Old Testament.
It is unclear whether Jesus actually quoted from the Greek Septaigant, or from the Hebrew version of the scriptures. There are no quotes by Jesus - or any New Testament author - from the 9 additional books of the Septaigant. So it is possible the Jesus was quoting from it, but from the Jewish Torah (same as the Protestant Old Testament). But because the gospels were written in Greek, the authors quoted from the Septaigant rather that create their own translation of the scripture that Jesus quoted.
All Old Tesament quotes by the other NT authors are taken from the Septaigant. Partly because it was the most commonly used translation of it day. But also because the authors were writing in Greek to Greek speaking/reading audiences. So it made sense to quote the OT in Greek, and to use the currently popular version instead of creating their own.
The Septaigant contains the same books as the Catholic Old Testament, but in a slightly different arrangement. OForo example, it combines the books of 1 and 2 Samuel into a single book, as well as 1 and 2 Kings in a single book and 1 and 2 Chronicles into a single book. Orignally each was a single book, but they were divided so that they could be put onto smaller scrolls, making them easier to handle.
It also uses slightly different names for some of the books, which is why there is a difference in the names of some of the OT books between the Catholic and Protestant Bibles. None of the books were originally named by their authors. The names have been added over the centuries by tradition.
The Jewish people did place a higher improtance on the first 5 books of the Torah. In fact, technically, the word Torah only refers to those five books. The complete collection of the Hebrew scriptures is called the Tanack, which combines the letters for Hebrews words for Law (Torah), Writings (or Psalms) and Prophets, and refers to the three division the Jews made in their scriptures.
Some Jews, such as the Suddacees of Jesus day, only considered the Torah (first five books) to be scripture. While other groups like the Pharisees included everything we know as the Old Testament today. So what was considered "scripture" varied with the group you were talking about.
Jesus appeared to be in line with the Pharisees, as he quoted from not just the Torah, but also the Wrtings and Prophets as if they were scripture. He referred more than once to "the law, the psalms, and the prophets". He also stated that the "traditions" of men made the laws of God of no effect. This is seen as a rejection of the "Talmud" which means "traditions", which was a series of writings that interpeted and added to the Torah. Jesus rejected those as been "scripture".