Reference: Fataawa ash-Shaykh al-‘Allaamah Muhammad Naasiruddeen al-Albaanee fil-Madeenah wal-Imaaraat – Page 95
Question: When should the [index] finger be moved during the tashahhud?
Response: [With respect to] the Sunnah, then no hadeeth exists stipulating it (the index finger) be raised [specifically]* when «أشهد أن لا إله إلا الله» is uttered.
[Therefore] because of that, the hadeeth of Waa.il ibn Hajar remains safe from any contradicting hadeeth; Bearing in mind, those who hold this* opinion, do so based upon [mere] conjecture, ijtihaad and istinbaat.
And that which there is no doubt about, is that the guiding and structured principles of the scholars [dictate] there is no ijtihaad in the presence of [the] authentic text [of the Qur.aan and the Sunnah].
So, there [we have] the hadeeth of Waa.il [which] describes his (sal-Allaahu ‘alayhi wa sallam)’s moving of his [index] finger from the beginning of his [tashahhud] sitting [right through] until his tasleem; [In conclusion therefore], it is not permissible to contradict this plain and clear Sunnah with any istinbaat.
 Transmitted by Ahmad 4/318, Abu Daawood 726-728, an-Nasaa.ee 2/127 and Ibn Maajah 810.