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, sallallaahu ʻalayhi wa sallam, is His slave and Messenger.
The Sunnah includes raising the index finger during the Tashahhud, supplicating until the end of the Tashahhud and then concluding the prayer with Tasleem. It has been reported that Waa’il ibn Hajar said pertaining to the description of the Prophet's prayer, “Then, he, sallallaahu ʻalayhi wa sallam, raised his finger and I saw him moving it, supplicating with it.” [Ahmad and An-Nasaa’i - Al-Albaani graded it Saheeh (sound)]
Moreover, Ibn Baaz said: “As for the index finger, the Sunnah includes raising it during the Tashahhud, from the beginning of the sitting until the Tasleem. It should be raised with a slight curve so as to point to the oneness of Allaah.” [Majmoo‘ Al-Fataawa]
Allaah Knows best.