"He (sallallaahu 'alaihi wa sallam) would spread his left palm on his left knee, clench all the fingers of his right hand, point with the finger adjacent to the thumb towards the qiblah, and fix his sight on it (i.e. the finger)."
Muslim, Abu Awaanah & Ibn Khuzaimah. Humaidi (13/1) and Abu Yalaa (275/2) added with a saheeh sanad on the authority of Ibn `Umar: "and this is the shooting of the devil; no-one will forget when he does this", and Humaidi raised his finger. Humaidi also said that Muslim bin Abi Maryam said, "A man related to me that in a church in Syria, he saw images of Prophets depicted like this", and Humaidi raised his finger. This is an extremely strange remark, but its sanad up to "the man" is saheeh.
Also, "when he pointed with his finger, he would put his thumb on his middle finger"
Muslim & Abu `Awaanah.
and sometimes "he would make a circle with these two."
Abu Daawood, Nasaa'i, Ibn al-Jaarood in al-Muntaqaa (208), Ibn Khuzaimah (1/86/1-2) & Ibn Hibbaan in his Saheeh (485) with a saheeh sanad. Ibn al-Mulaqqin also declared it saheeh (28/2), and it has a supporting narration in Ibn `Adi (287/1).
"When he raised his finger, he would move it, supplicating with it"
ibid. About "supplicating with it", Imaam Tahaawi said, "This is evidence that it was at the end of the prayer." Hence, there is evidence in this that the Sunnah is to continue pointing and moving the finger until the tasleem, for the supplication is until then. This is the view of Maalik and others. Imaam Ahmad was asked, "Should a man point with his finger during prayer?" He replied, "Yes, vigorously." (Mentioned by Ibn Haani in his Masaa'il of Imaam Ahmad, 1/80). From this, it is clear that moving the finger in tashahhud is a proven sunnah of the Prophet (sallallaahu alaihi wa sallam), and it was practised by Ahmad and other imaams of the Sunnah. Therefore, those who think that it is pointless and irrelevant and has nothing to do with the Prayer, should fear Allaah, since because of this, they do not move their fingers although they know it to be an established sunnah; and they take great pains to interpret it in a way which is inconsistent with theArabic way of expression and contrary to the understanding of the imaams with regard to it.The amazing thing is that some of them will defend an imaam on other issues, even if his opinion conflicts with the Sunnah, with the argument that to point out the imaam's mistakes inevitably means to taunt and disrespect him. They then forget this and reject this established sunnah, at the same time mocking at those who practise it. Whether or not they realise it, their mockery also includes those imaams whom they often defend wrongly, and who are correct about the Sunnah this time! In fact, they are deriding the Prophet (sallallaahu `alaihi wa sallam) himself, for he is the one who brought us this sunnah, and so jeering at it is equivalent to jeering at him. << But what is the reward for those among you who behave like this except ... >>
As for putting the finger down after pointing, or limiting the movement to the affirmation (saying laa ilaaha: 'there is no god ...') and negation (saying: illallaahu: '... except Allaah'), all of that has no basis in the Sunnah; in fact, it is contrary to the Sunnah, as this hadeeth proves.
Further, the hadeeth that he would not move his finger does not have an authentic isnaad, as I have explained in Da`eef Abi Daawood (175). Even if it were authentic, it is negatory, while the hadeeth above is affirmatory: the affirmatory takes precedence over the negatory, as is well-known among the scholars.
and he used to say, "It is surely more powerful against the devil than iron, meaning the forefinger."
Ahmad, Bazzaar, Abu Jafar al-Bukhteeri in al-Amaali (60/1),Abdul Ghani al-Maqdisi in his Sunan (12/2) with a hasan sanad, Rooyaani in his Musnad (249/2) & Baihaqi.
Also, "the Companions of the Prophet (sallallaahu 'alaihi wa sallam) used to remind each other, that is, about pointing with the finger when supplicating."
Ibn Abi Shaibah (2/123/2) with a hasan sanad
Once, "he saw a man supplicating with two fingers, so he said, "Make it one, [make it one,]" and indicated with his forefinger."
Ibn Abi Shaibah (12/40/1, 2/123/2) & Nasaa'i . Haakim declared it saheeh and Dhahabi agreed, and there is a supporting narration for it in Ibn Abi Shaibah.
"He (sallallaahu 'alaihi wa sallam) would do this in both tashahhuds."
Nasaa'i & Baihaqi with a saheeh sanad.
You should read 'The Prophet's Prayer Described' By Shaykh Muhammad Naasir-Ud-Deen Al-Albaanee, i'd have to say that this is the most authentic prayer book out there .
Allahu Alim
'Rabbee zidnee`ilmaa'
My Lord! Increase me in knowledge.[20:114]
The Prophet (sallallaahu 'alayhe wa sallam) said:
"Whoever sets out on a path to seek knowledge, Allaah will make easy his path to Paradise."
[Saheeh Muslim]