The Tree Trunk
In Medina Muhammad used to deliver sermons leaning on a tree stump. When the number of worshippers increased, someone suggested a pulpit be built so he can use it to deliver the sermon. When the pulpit was built, he abandoned the tree trunk. Abdullah ibn Umar, one of the companions, gave an eye-witness testimony of what happened. The trunk was heard weeping, the Prophet of mercy went towards it and comforted it with his hand. 
The event is also confirmed through eye-witness testimony transmitted through the ages with an unbroken chain of reliable scholars ( hadith mutawatir ). 
The Flowing of Water
On more than one occasion when people were in dire need of water, the blessing of the Muhammad saved them. In the sixth year after the he migrated from Mecca to Medina, Muhammad went to Mecca for pilgrimage. In the long journey through the desert, people ran out of all water, only the Prophet was left with a vessel with which he performed ablution for prayers. He put his hand in the vessel, water began flowing from between his fingers. Jabir ibn Abdullah, who witnessed the miracle, says of the fifteen hundred men, ‘We drank it and made ablution.’  This miracle has been transmitted with an unbroken chain of reliable scholars ( hadith mutawatir ). 
The sprouting of water from human fingers is similar to the Moses’ miracle of producing water from a rock.
Blessing of Food
On more than one occasion, the Prophet blessed food by either praying or touching it so all present could get their fill. This happened at times when food and water shortage afflicted Muslims.  These miracles took place in the presence of a large number of people and is, thus, not possible to deny.
Healing the Sick
Abdullah ibn Ateek broke his leg and Muhammad healed it by wiping his hand over it. Abdullah said it was as if nothing had happened to it! The person who witnessed the miracle was another companion, Bara’ ibn Azib (Saheeh Al-Bukhari)
During the expedition of Khyber, Muhammad healed the painful eyes of Ali ibn Abi Talib in front of a whole army. Ali, many years later, became the fourth caliph of Muslims. 
Muhammad exorcised the devil out of a boy brought by his mother for healing to him by saying, ‘ Come out! I am Muhammad, the Messenger of God! ’ The woman said, ‘By the One who sent you with the truth, we have never seen anything wrong with him since.’ 
(1) The mother of Abu Hurayra, a close companion of Muhammad, used to speak ill of Islam and its prophet. One day, Abu Hurayra came weeping to Muhammad and asked him to pray for his mother to be saved. Muhammad prayed and when Abu Hurayra returned home he found his mother ready to accept Islam. She bore the testimony of faith in front of her son and entered Islam. 
(2) Jarir ibn Abdullah was commissioned by the Prophet to rid the land of an idol worshipped besides God, but he complained he was could not ride a horse well! The Prophet prayed for him, ‘O God, make him a strong horseman and make him one who guides and is guided .’ Jarir testifies he never fell off his horse after the Prophet prayed for him. 
(3) The people were struck with famine during the time of Muhammad. A man stood up when Muhammad was delivering the weekly sermon on Friday, and said, ‘O Messenger of God, our wealth has been destroyed and our children are starving. Pray to God for us.’ Muhammad raised his hands in prayer.
Those in attendance testify that that the moment he lowered his hands after praying, clouds began to build like mountains!
By the time he stepped down off his pulpit, rain was dripping from his beard!
It rained the whole week till next Friday!
The same man stood up again, complained this time, ‘O Messenger of God, our buildings are destroyed, and our property is drowned, pray to God for us!’
Muhammad raised his hands and prayed, ‘O God, (let it rain) around us, but not on us.’
Those in attendance testify that the clouds withdrew in the direction he pointed, the city of Medina was surrounded by clouds, but there were no clouds over it! 
(4) Here is the beautiful story of Jabir. He testifies that one time, the camel he was riding was exhausted because it was used for carrying water. The camel could hardly walk. Muhammad asked him, ‘What’s the matter with your camel?’ On finding out how tired the poor camel was, Muhammad prayed for the poor animal and from that time, Jabir tells us, the camel was always ahead of others! Muhammad asked Jabir, ‘How do you find your camel?’ Jabir responded, ‘It is well, your blessing has reached it!’ Muhammad bought the camel from Jabir on the spot for a piece of gold, with the condition that Jabir ride it back to the city! On reaching Medina, Jabir says he brought the camel to Muhammad the next morning. Muhammad gave him the piece of gold and told him to keep his camel! 
It is no wonder why those around him who witnessed these great miracles performed in front of crowds were certain of his truthfulness.