The Prophet (ﷺ) said: Your Lord is munificent and generous, and is ashamed to turn away empty the hands of His servant when he raises them to Him.
Sunan Abi Dawud Book 8, Hadith 73
← Previous Hadith I saw the Messenger of Allah (ﷺ) supplicating Allah in this manner with the palms of his hands and also with their backs upwards.

Sunan Abi Dawud Book 8, Hadith 72 Next Hadith → 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.

Sunan Abi Dawud Book 8, Hadith 74