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Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
abudawud:1487 – ʿUqbah b. Mukram > Salm b. Qutaybah > ʿUmar b. Nabhān > Qatādah > Anas b. Mālik

I saw the Messenger of Allah ﷺ supplicating Allah in this manner with the palms of his hands and also with their backs upwards.  

أبو داود:١٤٨٧ – حَدَّثَنَا عُقْبَةُ بْنُ مُكْرَمٍ حَدَّثَنَا سَلْمُ بْنُ قُتَيْبَةَ عَنْ عُمَرَ بْنِ نَبْهَانَ عَنْ قَتَادَةَ عَنْ أَنَسِ بْنِ مَالِكٍ قَالَ

رَأَيْتُ رَسُولَ اللَّهِ ﷺ يَدْعُو هَكَذَا بِبَاطِنِ كَفَّيْهِ وَظَاهِرِهِمَا  

See similar narrations below:

Collected by Aḥmad
ahmad:11103 – Ḥasan > Ḥammād b. Salamah > Bishr b. Ḥarb > Abū Saʿīd al-Khudrī

[Machine] I saw the Messenger of Allah, ﷺ , making this supplication at Arafat and he placed the palms of his hands pointing downwards towards the ground.  

أحمد:١١١٠٣ – حَدَّثَنَا حَسَنٌ حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ عَنْ بِشْرِ بْنِ حَرْبٍ عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ قَالَ

رَأَيْتُ رَسُولَ اللهِ ﷺ بِعَرَفَةَ يَدْعُو هَكَذَا وَجَعَلَ بَاطِنَ كَفَّيْهِ مِمَّا يَلِي الْأَرْضَ