All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
The book "Awjaz Al-masaalik Ilaa Muwatta' Maalik" is authored by the prominent scholar Muhammad Zakariyyaa Al-Kandahlawi . When discussing the issue of moving the index in Tashahhud, he quoted the words which were mentioned in the question from the book "Kashful Ghummah."
However, saying that "Kashful Ghummah" may be from the books of Shiites is very unlikely because the author is a well-known Sunni scholar, and it is impossible that he would report something from the Raafidhah (Shiites) books.
Furthermore, the Raafidhah are more unlikely to report or give evidence for their actions or statements based on the actions and statements of the companions, like Ibn Az-Zubayr .
Nonetheless, we think that the book which is mentioned in the question is the book entitled "Kashful Ghummah 'An Jamee' Al-ummah" authored by the prominent scholar 'Abdul-Wahhaab Ash-Sha'raani . This is a book on jurisprudence from which the scholars usually quote.
As regards the evidence of the narration of Ibn Az-Zubayr, it is reported by Abu Daawood and An-Nasaa'ee as narrated by 'Abdullaah Ibn Az-Zubayr that the Prophet used to point with his index finger when supplicating but he never used to move it.
However, the narration of Waa'il Ibn Hujr is contradictory to the above as he described the method of the prayer of the Prophet and mentioned the position of putting the hands in Tashahhud, saying: "…Then he raised his (index) finger, and I saw him moving it while supplicating." [Abu Khuzaymah and Al-Bayhaqi]
Allaah Knows best.