Musnad Abu Ya'la al-Mawsili 148:60

Abu Bakr ibn Abi Shaybah narrated to us, Yazid ibn Harun narrated to us, from al-Awwam ibn Hawshab, who said: Sulayman ibn Abi Sulayman, the freed slave of Ibn Abbas, narrated to me, from Anas ibn Malik, that the Messenger of Allah (may Allah bless him and grant him peace) said: "When Allah created the earth, it began to sway, so He created the mountains and cast them upon it, and it became stable. The angels were amazed at the creation of the mountains and said: 'O Lord, is there anything in Your creation stronger than the mountains?' He said: 'Yes, iron.' They said: 'O Lord, is there anything in Your creation stronger than iron?' He said: 'Yes, fire.' They said: 'O Lord, is there anything in Your creation stronger than fire?' He said: 'Yes, water.' They said: 'O Lord, is there anything in Your creation stronger than water?' He said: 'Yes, the wind.' They said: 'O Lord, is there anything in Your creation stronger than the wind?' He said: 'Yes, the human being who gives charity with his right hand, concealing it from his left.'"