The Holy Prophet sas would sometimes raise his hands for prayer, and we follow that example. For example:
While the Prophet(Sahih al-Bukhari, Book 11, Hadith 56)
saswas delivering the khutbah [sermon] on a Friday, a man stood up and said, “O, Allah’s Apostle! The livestock and the sheep are dying, so pray to Allah for rain.” So he sas raised both his hands and invoked Allah (for it).
A companion narrates:
I told the Prophet(Sahih al-Bukhari, Book 64, Hadith 353).
sasabout our and Abū Amir’s news and how he had said, “Tell him to ask for Allah’s Forgiveness for me.” The Prophet sasasked for water, performed ablution and then raised his hands, saying, “O Allah’s Forgive Ubaid, Abu Amir.” At that time I saw the whiteness of the Prophet’s sas armpits.
Another companion narrates:
When we reached the Prophet(Sahih al-Bukhari, Book 64, Hadith 368)
sas, we mentioned to him the whole story. On that, the Prophet sas raised both his hands and said twice, “O Allah! I am free from what Khalid has done.”