Sunan Abu Dawud
1489
Sahih+3

Narrated Abdullah ibn Abbas: Ikrimah quoted Ibn Abbas as saying: When asking for something you should raise your hands opposite to your shoulders; when asking for forgiveness you should point with one finger; and when making an earnest supplication you should spread out both your hands

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid