Sunan Abi Dawud 1487
سنن أبي داود#1487Sahihحَدَّثَنَا عُقْبَةُ بْنُ مُكْرَمٍ، حَدَّثَنَا سَلْمُ بْنُ قُتَيْبَةَ، عَنْ عُمَرَ بْنِ نَبْهَانَ، عَنْ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَدْعُو هَكَذَا بِبَاطِنِ كَفَّيْهِ وَظَاهِرِهِمَا .
Narrated Anas ibn Malik: I saw the Messenger of Allah (ﷺ) supplicating Allah in this manner with the palms of his hands and also with their backs upwards
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Shuaib Al ArnautSahih Lighairihi
Zubair Ali ZaiDaif
In-book reference: 8:72