Sorry, but that is complete and utter nonsense.
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Not so, my friend.
Of course they are only recorded in the Christian Holy Scriptures. It is the New Testament of Jesus Christ.
For the wages of sin is death, but the gift of God is eternal life through Jesus Christ, our Lord. Romans 6:23
It should be simple, then, for you to provide me with any objective evidence that the Pharisees and the Sadducees "did not know the prophetic scriptures".
Of course they are only recorded in the Christian Holy Scriptures.
Which, I submit, cannot be used as an unbiased source of information about 1st century Judaism.