It is mustahabb to continue pointing with the finger during the tashahhud until the second tasleem is complete
Question

                During the tashahhud and after the individual has finished reciting the salaah Ibraaheemiyyah, should the forefinger remain raised until the imam says the tasleem, or can he open his clenched fingers and put them on his thigh as soon as he has finished the salaah Ibraaheemiyyah?
Praise be to Allah.
    Firstly: 

    It is proven in the Sunnah, in the description of the prayer 
    of the Prophet (blessings and peace of Allah be upon him) that the 
    forefinger should be raised during the tashahhud in the prayer. This issue 
    has been discussed in detail, with evidence, in the answer to questions no.
    7570 and
    11527 

    The fuqaha’ stated that the one who points with his 
    forefinger during any part of the tashahhud has basically fulfilled the 
    Sunnah and has followed the teaching of the Prophet (blessings and peace of 
    Allah be upon him) in his prayer. Rather the discussion is about choosing 
    the point at which one should raise the forefinger; which point is best? 

    Shaykh Ahmad al-Barlasi ‘Umayrah ash-Shaafa‘i (d. 957) said: 

    Whatever the worshipper does of the ways that are mentioned, 
    he has fulfilled the Sunnah. Rather the difference of opinion is concerning 
    which option is best.

    End quote from Haashiyat ‘Umayrah, 1/188. See also: 
    al-Majmoo‘ by an-Nawawi, 3/434. 

    This difference of opinion as to which option is best is the 
    matter of ijtihaad and is subject to further examination, because there is 
    no clear text that has been narrated concerning this topic. 

    In the hadeeth of Ibn ‘Umar (may Allah be pleased with him) 
    it says that when the Prophet (blessings and peace of Allah be upon him) sat 
    during the prayer, he would place his right hand on his knee and raise the 
    finger that is next to the thumb, offering supplication with it, and his 
    left hand rested flat on his knee. 

    Narrated by at-Tirmidhi (no. 249). He said: The hadeeth of 
    Ibn ‘Umar is a hasan ghareeb hadeeth; we do not know of it from the hadeeth 
    of ‘Ubaydullah ibn ‘Umar except via this isnaad. It is to be followed 
    according to some of the scholars among the Companions of the Prophet 
    (blessings and peace of Allah be upon him) and the Taabi‘een, who favoured 
    the view that one should point during the tashahhud. This is also the view 
    of our companions. End quote. 

    It was also classed as saheeh by Shaykh al-Albaani in 
    Saheeh at-Tirmidhi. 

    The words “and raise the finger that is next to the thumb, 
    offering supplication with it” indicate that raising of the finger begins 
    when reciting the supplication (du‘aa’) in the tashahhud, and the 
    supplication begins with the twin declaration of faith (ash-shahaadatayn), 
    because of what it contains of acknowledgement and affirmation of the 
    Oneness of Allah, may He be glorified and exalted, and that is more likely 
    to be accepted. Then after that, he begins to recite the supplication 
    referred to: “Allaahumma salli ‘ala Muhammad … (O Allah, send 
    blessings upon Muhammad…” until the end of the tashahhud, and until he has 
    completed the tasleem. With regard to the beginning of the tashahhud (“at-tahiyyaatu 
    Lillahi… (all compliments… are due to Allah”)) until we say “… wa 
    ‘ala ‘ibaad illaahi’s-saaliheen (and upon the righteous slaves of 
    Allah”), this is not part of the supplication; rather these are words of 
    praise to Allah and greetings of salaam to His slaves. 

    The reports narrated from the Sahaabah and Taabi‘een 
    concerning this matter indicate that what is meant by pointing with the 
    forefinger is an indication of affirmation of Allah’s Oneness (Tawheed) and 
    sincerity. Pointing with one finger is a practical declaration of faith in 
    Allah, the One, Who has no partner or associate. So it is appropriate that 
    starting to point with it should come when starting to say the words of the 
    shahaadah or declaration of faith (“Ashhadu an laa ilaaha ill-Allah 
    (I bear witness that there is no god but Allah)).” 

    Hence Ibn ‘Abbaas (may Allah be pleased with him) said: That 
    is sincerity. 

    Ibraaheem an-Nakha‘i (may Allah have mercy on him) said: If a 
    man points with his finger during the prayer, it is good and it is an 
    affirmation of the Oneness of Allah (Tawheed).

    Narrated by Ibn Abi Shaybah in at-Tasannuf, 2/368 

    This is the view of those fuqaha’ who said that pointing with 
    the forefinger should begin when reciting the declaration of belief in the 
    Oneness of Allah. 

    As for when to stop (pointing with the finger), the Sahaabah 
    who described the raising of the forefinger did not say that the Prophet 
    (blessings and peace of Allah) lowered it; therefore it should be kept 
    raised until one has finished the tasleem, especially since the latter part 
    of the tashahhud is all supplication (du‘aa’). 

    Abu ‘Abdullah al-Khurashi al-Maaliki (d. 1101 AH – may Allah 
    have mercy on him) said: 

    From the beginning of the tashahhud until the end, which is 
    (saying) “Ashhadu an laa ilaaha ill-Allah wa anna Muhammadan ‘abduhu wa 
    rasooluhu (I bear witness that there is no God but Allah and that 
    Muhammad is His slave and Messenger)”, and in accordance with what they 
    said, it should continue until the salaam, even if the tashahhud is 
    lengthy. 

    End quote from Sharh Mukhtasar Khaleel, 1/288. 

    Ash-Shaafa‘i agreed with them that pointing should only begin 
    with the Shahaadatayn (twin declaration of faith), but they addressed the 
    issue in more precise detail, and that may require proof. They said: 
    Starting to raise the finger should only come when reaching the hamzah in 
    the phrase in the shahaadatayn “ila-Allah (but Allah)”. 

    Imam an-Nawawi (may Allah have mercy on him) said: 

    According to all opinions and views, it is mustahabb to point 
    with the right forefinger, raising it when reaching the hamzah in the phrase 
    Laa ilaaha ill-Allah.

    End quote from al-Majmoo‘ Sharh al-Muhadhdhab, 3/434 

    Imam ar-Ramli ash-Shaafa‘i (may Allah have mercy on him) 
    said: 

    He should raise it when saying “illa-Allah (but Allah)”; he 
    should  begin to raise his finger at the hamzah, thus following what was 
    narrated by Muslim… which clearly indicates that it should remain raised 
    until he stands up (for a third rak‘ah) or says the salaam. What some later 
    scholars tried to prove about lowering it is contrary to what has been 
    narrated.

    End quote from Nihaayat al-Muhtaaj, 1/522 

    Some of the scholars said that pointing with the finger 
    should start from the beginning of the tashahhud, because the entire 
    tashahhud is a supplication, and it is proven in the hadeeth that he (the 
    Prophet (blessings and peace of Allah be upon him)) used to offer 
    supplication with it. The words at the beginning of the tashahhud (“At-Tahiyyaatu 
    Lillahi…”) are words of praise before offering supplication, so it is 
    part of the supplication and is not something separate. 

    Shaykh al-Islam Ibn Taymiyyah (may Allah have mercy on him) 
    said: It is mustahabb to point with one finger during the tashahhud and 
    supplication (du‘aa’). 

    Al-Ikhtiyaaraat, 38. 

    It says in Fataawa al-Lajnah ad-Daa’imah (7/56): 

    Pointing with the finger throughout the tashahhud and moving 
    it when offering supplication (du‘aa’), and clenching the other fingers 
    should continue until the salaam. End quote. 

    Whatever the case, the matter is subject to ijtihaad and is 
    something concerning which the scholars differed. The different opinions 
    concerning it may have to do with slight differences in the way the prayer 
    is performed, so there is nothing wrong with differing from this ijtihaad 
    and following what one thinks is more correct on the basis of evidence. 

    It also says in Fataawa al-Lajnah ad-Daa’imah 
    (5/368): 

    Raising the forefinger in the tashahhud is Sunnah, and the 
    reason behind it is to indicate the Oneness of Allah. Whoever wishes may 
    move it and whoever wishes may not move it. This matter should not lead to 
    division and discord between seekers of knowledge. If a person does not 
    raise it at all, or he raises it but does not move it, this is a minor 
    matter that should not lead to denunciation and resentment. However the 
    Sunnah is to raise it throughout the shahaadatayn, until the worshippers 
    says the salaam, as an affirmation of divine Oneness. With regard to moving 
    it, that should be when reciting the supplication, as is narrated in the 
    saheeh Sunnah. 

    End quote from Fataawa al-Lajnah, 5/368 

    And Allah knows best.