Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear brother in Islam, thanks a lot for your question, which shows your keenness on abiding by Allah’s laws and teachings. May Allah enlighten our hearts with the light of Islam!
It is preferable sunnah to point with the forefinger and move it during the tashahhud.
Elaborating more on this, We would like to cite the following published on www.islamqa.info:
It is sunnah to point with the forefinger and move it during the tashahhud because of the report narrated by Ahmad and An-Nasa’i from Wa’il ibn Hajar who said: I said, “I will watch how the Messenger of Allah (peace and blessings be upon him) prays. So I watched him and he stood up and said “Allahu akbar” and raised his hands until they were level with his ears, then he placed his right hand over his left and left wrist and left forearm. Then when he wanted to bow he raised his hands likewise. He put his hands on his knees, when he raised his head he raised his hands likewise. Then he prostrated and put his hands level with his ears, then he sat resting on his left foot and placed his left hand on his thigh and left knee, and he put the elbow of his right hand on his right thigh. Then he made a circle with two of his fingers, then he raised his finger and I saw him moving it and making du`aa’ with it.”
Imam Muslim narrated that `Abdullah ibn `Umar said, “When he, the Prophet (peace and blessings be upon him), sat during the Prayer, he would place his right hand on his right thigh and clench all his fingers, and point with the finger that is next to the thumb, and he would place his left hand on his left thigh.”
According to a report narrated by Muslim from Ibn `Umar, when the Prophet (peace and blessings be upon him) sat during the Prayer, he would put his hands on his thighs and raise the finger of his right hand that is next to the thumb, and make du`aa’ with it, and his left hand would be resting on his left thigh.
An-Nasa’i narrated that Sa`d said: The Messenger of Allah (peace and blessings be upon him) passed by me while I was making du`aa’ with my fingers and he said, “One, one,” and pointed with his index finger. Meaning: point with one finger, namely the index finger.
Imam Ahmad narrated that Nafi` said, “When `Abdullah ibn `Umar sat during the Prayer, he would put his hands on his thighs and point with his finger while looking at it. Then he said, ‘Allah’s Messenger (peace and blessings be upon him) said, “It is harder on Satan than iron, (meaning the index finger).”
These Hadiths indicate two things:
1- That one should point with the finger throughout the entiretashahhud.
2- That one should move it when making du`aa’.
The late Sheikh Ibn `Uthaymeen, a prominent Saudi Muslim scholar, (may Allah shower mercy on his soul), explained the phrases narrated for the du`aa’ in the tashahhud. He said,
Every time you make du`aa’, then move your finger upward toward the One upon Whom you are calling, so we say:
“As-salamu `alayka ayyuha-n-Nabiyyu” (Peace be upon you, Prophet). You should point your finger while reciting this because the salam is a kind of du`aa’.
“As-salamu `alayna” (Peace be upon us). Point your finger.
“Allahumma salli `ala Muhammad” (O Allah, send prayers upon Muhammad), point your finger.
“Allahumma barik `ala Muhammad” (O Allah, send blessings upon Muhammad), point your finger.
“A`udhu billahi min `adhaab jahannam” (I seek refuge with Allah from the torment of Hell), point your finger.
“Wa min `adhaab il-qabr” (And from the torment of the grave), point your finger.
“Wa min fitnat il-mahyaa wal-mamaat” (And from the trials of life and death), point your finger.
“Wa min fitnat il-maseeh il-dajjal” (And from the trial of the Dajjal), point your finger.
Every time you make du`aa’, point upward toward the One upon Whom you are calling. This is closer to the Sunnah.
Allah Almighty knows best.