Allah T'ala says in the Holy Quran:
Muhammad (s.a.a.w.) was of a height a little above the average. He was of sturdy build with long muscular limbs and tapering fingers. The hair of his head was long and thick with some waves in them. His forehead was large and prominent, his eyelashes were long and thick, his nose was sloping, his mouth was somewhat large and his teeth were well set. His cheeks were spare and he had a pleasant smile. His eyes were large and black with a touch of brown. His beard was thick and at the time of his death, he had seventeen grey hairs in it. He had a thin line of fine hair over his neck and chest. He was fair of complexion and altogether was so handsome that Abu Bakr composed this couplet about him:
"As there is no darkness in the moonlit night so is Mustafa, the well-wisher, bright."
His gait was firm and he walked so fast that others found it difficult to keep pace with him. His face was genial but at times, when he was deep in thought, there there were long periods of silence, yet he always kept himself busy with something. He did not speak unnecessarily and what he said was always to the point and without any padding. At times he would make his meaning clear by slowly repeating what he had said. His laugh was mostly a smile. He kept his feelings under firm control - when annoyed, he would turn aside or keep silent, when pleased he would lower his eyes [Tirmidhi].
His dress generally consisted of a shirt, tamad (trousers), a sheet thrown round the shoulders and a turban. On rare occasions, he would put on costly robes presented to him by foreign emissaries in the later part of his life. [Ahmed, Musnad, Hafiz Bin Qayyim]
His blanket had several patches. [Tirmidhi] He had very few spare clothes, but he kept them spotlessly clean. [Bukhari] He wanted others also to put on simple but clean clothes. Once he saw a person putting on dirty clothes and remarked,
"Why can't this man wash them." [Abu Dawood]
On another occasion he enquired of a person in dirty clothes whether he had any income. Upon getting a reply in the affirmative, he observed,
"When Allah has blessed you with His bounty, your appearance should reflect it." [Abu Dawood]
He used to observe:
"Cleanliness is piety."
Reference url: http://muslim-canada.org/muhammadatharhusain.html
The nation of Thamud comes after the 'Aad people as the worst transgressors. Basically, their deviation was the same as of the people of Hazrat Nuh and the 'Aad. They also believed in the existence of Allah and His being the Ilah and the Rabb but they did not agree that He was the only ilah, that He alone was worthy of all 'ibadah, and that He was Rabb in all the senses of the word. They insisted that there were others, besides Allah, who too could accept prayers, grant favors, and remove distress, and in moral and cultural matters they took their law from their chiefs and priests instead of following Divine guidance. It was this which made them into a tragically misled people and brought down on them Allah's punishment:
And (O' Muhammad) if they turn away (and do not listen to what you say) then say to them: I am warning you of a punishment the like of that which visited the 'Aad and the Thamud, to whom Prophets came repeatedly telling them not to give their 'ibadah to any but Allah, and whose only reply was: 'If our Rabb had wanted, He would surely have sent down angels, (but since He did not), we reject the message which you bring'. (Quran 14:13-14)
And to the Thamud (we sent) their kinsman Saleh, who said to them, "O' my People: 'give your 'ibadah to Allah; you have no ilah but He."...They replied, "O' Saleh, we had great hopes of you (and now you spear strangely); Do you mean to forbid us to give our 'ibadah to those to whom our ancestors used to give their?" (Quran 11:61-62)
When their kinsman Saleh said to them: "Do you not fear (God)? I am verily an apostle worthy of trust where fore fear God, and obey me and not obey all the words of transgressors who cause strife in the land and who do not mend their ways." (Quran 26:142-143, 150-152).