Authentic
Sunan Abu Dawud 1486
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).
إِذَا سَأَلْتُمُ اللَّهَ فَاسْأَلُوهُ بِبُطُونِ أَكُفِّكُمْ وَلاَ تَسْأَلُوهُ بِظُهُورِهَا "