"My father told me: 'I prayed behind the Messenger of Allah (ﷺ) and I saw him raise his hands when he started to pray, and when he bowed, and when he said: Sami' Allahu liman hamidah (Allah hears the one who praises Him)" like this.'" And (one of the narrators) Qais pointed towards his ears.
The Book of The At-Tatbiq (Clasping One's Hands Together)
Sunan an-Nasa'i - Hadith 1055
Hadith Text
"My father told me: 'I prayed behind the Messenger of Allah (ﷺ) and I saw him raise his hands when he started to pray, and when he bowed, and when he said: Sami' Allahu liman hamidah (Allah hears the one who praises Him)" like this.'" And (one of the narrators) Qais pointed towards his ears.
Scholarly Commentary
This noble hadith establishes the Sunnah of raising the hands during prayer at three specific positions: at the opening takbir (takbirat al-ihram), when bowing into ruku', and when rising from ruku' while saying "Sami' Allahu liman hamidah." The gesture of Qais pointing to his ears indicates the hands should be raised to the level of the ears or shoulders.
Imam an-Nawawi states this is among the most authentic transmissions regarding hand-raising in prayer, with consensus among the four schools on its recommendation. The Malikis differ only in considering it recommended at the opening takbir and mustahabb (preferable) at other positions.
The wisdom behind this raising includes: glorifying Allah through physical action accompanying verbal remembrance, preparing the heart for prayer through bodily movements, and following the perfect example of the Prophet (ﷺ) in both word and deed.
Legal Ruling
The majority of scholars consider raising hands at these three positions to be Sunnah Mu'akkadah (emphasized tradition). While omitting it doesn't invalidate prayer, consistently abandoning it is reprehensible. The hands should be open with fingers naturally extended, not clenched, facing the qiblah.