Mishkat al-Masabih 1923
Anas reported God’s messenger as saying:
When God created the earth it began to oscillate, so He created the mountains, ordered them on to it, and it became steady. The angels marvelled at the strength of the mountains and asked their Lord whether there was anything in His creation stronger than the mountains, to which He replied that iron was stronger. 
They asked if anything in His creation was stronger than iron, and He replied that fire was. 
They asked if anything in His creation was stronger than fire and He replied that water was. 
They asked if anything in His creation was stronger than water and He replied that wind was. 
They asked if anything in His creation was stronger than wind and He replied, 
“Yes, the son of Adam who gives sadaqa with his right hand concealing it from his left.” 

Tirmidhi transmitted it, saying this is a gharib tradition.
وَعَن أنس بن مَالك عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «لَمَّا خَلَقَ اللَّهُ الْأَرْضَ جَعَلَتْ تَمِيدُ فَخَلَقَ الْجِبَالَ فَقَالَ بِهَا عَلَيْهَا فَاسْتَقَرَّتْ فَعَجِبَتِ الْمَلَائِكَةُ مِنْ شِدَّةِ الْجِبَالِ فَقَالُوا يَا رَبِّ هَلْ مِنْ خَلْقِكَ شَيْءٌ أَشَدُّ مِنِ الْجِبَالِ قَالَ نعم الْحَدِيد قَالُوا يَا رَبِّ هَلْ مِنْ خَلْقِكَ شَيْءٌ أَشَدُّ مِنَ الْحَدِيدِ قَالَ نَعَمِ النَّارُ فَقَالُوا يَا رب هَل من خلقك شَيْء أَشد من النَّار قَالَ نعم المَاء قَالُوا يَا رب فَهَل مِنْ خَلْقِكَ شَيْءٌ أَشَدُّ مِنَ الْمَاءِ قَالَ نَعَمِ الرِّيحُ فَقَالُوا يَا رَبِّ هَلْ مِنْ خَلْقِكَ شَيْءٌ أَشَدُّ مِنَ الرِّيحِ قَالَ نَعَمِ ابْن آدم تصدق بِصَدقَة بِيَمِينِهِ يخفيها من شِمَالِهِ» . رَوَاهُ التِّرْمِذِيُّ وَقَالَ: هَذَا حَدِيثٌ غَرِيبٌ
وَذُكِرَ حَدِيثُ مُعَاذٍ: «الصَّدَقَةُ تُطْفِئُ الْخَطِيئَةَ» . فِي كتاب الْإِيمَان