Is it Sunnah good for someone rounding off his ablution to put on his finger and touches his tongue before saying the "Shahadah"?

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.

As far as we know it is not from the Sunnah for a person to put his index finger on his tongue before uttering the testimony of faith after completing ablution. The Sunnah is what is reported by Imaam Muslim that the Prophet said: "None of you makes ablution thoroughly washing his organs, then says: "Ash-hadu allaa ilaaha illallaah wa anna Muhammadan 'abdu allaahi wa rassooluhu" (I bear witness that None has the right to be worshipped but Allaah and Mohammad is His slave and Messenger) except that the eight gates of Paradise open to him for him to enter through any of them he wishes." [Muslim].

Another narration reported by At-Tirmithi reads: "Whoever performs ablution properly washing his organs, then says: "Ash-hadu allaa ilaaha illallaah wahdahu laa shareeka lah, wa ash-hadu anna Muhammadan 'abduhu wa rassooluhu allaahumma ij'alnee mina at-Tawwaabeena waj'alnee mina al-Mutatahhireen" (I bear witness that None has the right to be worshipped but Allaah who has no partners or associates and I bear witness that Mohammad is His slave and Messenger, O, Allaah make me be among those who return to You in repentance and make me of those who remain clean and pure), except that the eight gates of Paradise open to him for him to enter through any of them he wishes."

Allaah knows best.