The entire OT is "law" and no one has shown otherwise. Again Rom 3:10-19 Paul cites Psalms and Isaiah calling both "law".
Lk 24:44 mentions the law of Moses, prophets and Psalms. Again Paul called Psalms prophet Isaiah Law.
Lk 16:16 refers to the OT as the law and prophests. Psalms was not a prophet book so it must fall under law.
britannica.com - Biblical literature - Old Testament canon, texts and versions...
The Hebrew Bible is often known among Jews as Tanakh, an acronym derived from the names of its three divisions being Torah (Instruction, or law also called the Pentateuch), Neviium (Prophets) and Ketuvim (Writings).
The Torah contains five books: Genesis, Exodus, Leviticus, Numbers and Deuteronomy
The Neviim comprise eight books divided into Former Prophets containing the four historical works Joshua, Judges, Samuel and Kings. (Notice there were no 1st or 2nd Samuel or Kings) The Latter Prophets, the oracular discourses of Isaiah, Jeremiah, Ezekiel, and the Twelve Minor Prophets, Hosea, Joel, Amos, Obadiah, Jonah, Micah, Nahum, Habakkuk, Zephaniah, Haggai, Zechariah and Malachi.
The Twelve were all formerly written on a single scroll thus reckond as one book. The Ketuvim consist of religious poetry and wisdom literature, Psalms, Proverbs and Job, a collection known as the Five Megillot (Five Scrolls; i.e., Song of Songs, Ruth, Lamentations, Ecclesiastes and Esther, which have been grouped together according to the annual cycle of their public reading in the synagogue) and the books of Daniel, Ezra, Nehemiah and Chronicles (No 1st or 2nd Chronicles).
You can read more at that website that goes into greater detail.
The whole OT is not law according to the break down I just gave. Psalms has nothing to do with the law as it's about poetry, song and music instruments according to the the Ketuvim. In the Tanakh (Hebrew Bible) there is no OT or NT as Jews would not recognize the Bible we use today as many Jewish writings were not added to our Bible.
Luke 24:44 And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me.
All things must be fulfilled as the law being fulfilled in Christ, the prophecies given by the prophets about Christ, and in the Psalms the life and ministry of Christ.
Luke 16:16 The law and the prophets were until John: since that time the kingdom of God is preached, and every man presseth into it.
The law and the prophets were until John baptized Jesus before His ministry began as a voice from heaven declared this is my beloved Son in whom I am well pleased, Matthew 3:13-17. Jesus came to fulfill the righteousness of the law, Matthew 5:17-20, preaching the kingdom of God as every man pressed in to hear His preaching.