Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
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
bayhaqi:6447 – Abū ʿAbdullāh al-Ḥāfiẓ > Abū Bakr b. Isḥāq al-Faqīh > Muḥammad b. Ayyūb > Abū Salamah And ʿAlī b. ʿUthmān > Ḥammād > Thābit > Anas b. Mālik

The Prophet ﷺ used to make supplication for rain in this manner. he spread his hands keeping the inner side (of hands) towards the earth, so I witnessed the whiteness of his armpits. (Using translation from Abū Dāʾūd 1171)   

البيهقي:٦٤٤٧ – وَأَخْبَرَنَا أَبُو عَبْدِ اللهِ الْحَافِظُ أنبأ أَبُو بَكْرِ بْنُ إِسْحَاقَ الْفَقِيهُ أنبأ مُحَمَّدُ بْنُ أَيُّوبَ أنبأ أَبُو سَلَمَةَ وَعَلِيُّ بْنُ عُثْمَانَ قَالَا ثنا حَمَّادٌ عَنْ ثَابِتٍ عَنْ أَنَسِ بْنِ مَالِكٍ

أَنَّ رَسُولَ اللهِ ﷺ اسْتَسْقَى فَقَالَ هَكَذَا وَمَدَّ يَدَيْهِ وَجَعَلَ بُطُونَهُمَا مِمَّا يَلِي الْأَرْضَ حَتَّى رَأَيْتُ بَيَاضَ إِبْطَيْهِ زَادَ عَلِيٌّ وَهُوَ عَلَى الْمِنْبَرِ  

See similar narrations below:

Collected by Abū Dāwūd
abudawud:1171 – al-Ḥasan b. Muḥammad al-Zaʿfarānī > ʿAffān > Ḥammād > Thābit > Anas

The Prophet ﷺ used to make supplication for rain in this manner. he spread his hands keeping the inner side (of hands) towards the earth, so I witnessed the whiteness of his armpits.  

أبو داود:١١٧١ – حَدَّثَنَا الْحَسَنُ بْنُ مُحَمَّدٍ الزَّعْفَرَانِيُّ حَدَّثَنَا عَفَّانُ حَدَّثَنَا حَمَّادٌ أَخْبَرَنَا ثَابِتٌ عَنْ أَنَسٍ

أَنَّ النَّبِيَّ ﷺ كَانَ يَسْتَسْقِي هَكَذَا يَعْنِي وَمَدَّ يَدَيْهِ وَجَعَلَ بُطُونَهُمَا مِمَّا يَلِي الأَرْضَ حَتَّى رَأَيْتُ بَيَاضَ إِبْطَيْهِ