The Prophet (ﷺ) said: When you make requests to Allah, do so with the palms of your hands, and not backs, upwards.

Abu Dawud said: The narrator Sulaiman b. 'Abd al-Hamid said: according to us Malik b. Yasar was a Companion of the Prophet (ﷺ).
Sunan Abi Dawud Book 8, Hadith 71
← Previous Hadith The Prophet (ﷺ) said: Do not cover the walls. He who sees the letter of his brother without his permission, sees Hell-fire.

Supplicate Allah with the palms of your hands; do not supplicate Him with their backs upwards. When you finish supplication, wipe your faces with them.

Abu Dawud said: This tradition has been transmitted through a different chains by Muhammad b. Ka'b; all of them are weak. The chain I have narrated is best of them; but it is also weak.

Sunan Abi Dawud Book 8, Hadith 70 Next 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