Positions of Raising Index Finger
23-6-2019 | IslamWeb
Question:
As-salaamu aleykum, I would like to know the Islamic meaning of pointing the index finger of the hand upwards. May Allaah bless you.
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad 
is His slave and Messenger.
You did not clarify to us – dear brother – the position of raising the index finger upwards. It was confirmed from the Prophet that he raised his index finger upwards in many situations, such as in Khutbah in the farewell message.
The Prophet said in the farewell message:
"And you would be asked about me (on the Day of Resurrection); (now tell me) what would you say?' They (the audience) said: 'We will bear witness that you have conveyed (the message), discharged (the ministry of Prophethood) and given wise (sincere) counsel.' He (the narrator) said: 'He (the Prophet) then raised his forefinger towards the sky and pointed it at the people (saying): 'O Allah, bear witness, o Allah, bear witness,' saying it thrice.'" [Muslim]
The interpreters of the Hadeeth stated that the Prophet raised his finger to the sky because it is the Kiblah (i.e. the direction) of supplication, and that he pointed it to the people to make Allah bear witness on them.
Also, the Prophet raised his index finger upwards in other positions, such as what was reported in the following Hadeeth.
‘Amar ibn al-‘Aas 
narrated: "We prayed with the Prophet one night [i.e. the Maghrib prayer], and there were some people who went back, and some others stayed [to wait for the ‘Ishaa' prayer]. Then the Prophet came back before people came back for the prayer; he came back in a hurry, out of breath, raising his finger showing number 29 and he pointed with his index finger to the sky while saying: 'Have glad tidings o Muslims, for your Lord has opened one of the Gates of heaven and is boasting of you before the angels, saying: 'Look at My slaves; they have fulfilled one obligatory prayer and they are waiting for another.'" [Ahmad]
Among other situations where the Prophet raised his index finger upwards is in Tashahhud in prayer. One of the Ahadeeth of the method of the prayer of the Prophet reads, "…When he sat in prayer [i.e. in Tashahhud], he placed his right hand on his knee, then he raised his index finger up to the sky supplicating with it." [At-Tirmithi, from the Hadeeth narrated by Ibn ‘Umar]
For more benefit, please refer to Fataawa 119138, 91001 and 81988.
Allah knows best.