Is raising one's hands and palms to the sky considered Sunnah during the Qunūt supplication, and what is its evidence?

Scholars have differed regarding the raising of hands in Du'a al-Qunut. The preponderant view is that it is a recommended act (mustahabb), whether it is Qunut al-Nazilah (Qunut for calamities) or Qunut al-Witr, because it is authentically reported that the Prophet (peace and blessings be upon him) raised his hands when supplicating against the polytheists who killed the seventy reciters during the Fajr prayer. This is as narrated by Anas (may Allah be pleased with him): "I indeed saw the Messenger of Allah (peace and blessings be upon him) in the Fajr prayer raising his hands and supplicating against them." As for Qunut al-Witr, it is because it is authentically reported from Umar and other Companions (may Allah be pleased with them) that they performed it, and they would not have done so except with evidence, and they used to pray behind the Prophet (peace and blessings be upon him), who said: "Pray as you have seen me praying."