the Fatwa Department Research Committee - chaired by Sheikh `Abd al-Wahhâb al-Turayrî
The `awrah of a man is between the navel and the knee. This is the area that has to be covered.
The Prophet (peace be upon him) said: “What is below his navel to his knee is his `awrah.” [Musnad Ahmad (6756), Sunan al-Dâraqutnî (1/230), and Sunan al-Bayhaqî (2/229)]
Both Shu`ayb al-Arna`ût and al-Albânî declare this hadîth to have a good (hasan) chain of transmission.
It is obligatory for every Muslim to cover his `awrah while in prayer. The `awrah for men is from the navel to the knee. As long as this area is thoroughly covered, prayer will be valid.
Scholars disagree, however, as to whether the knees themselves have to be covered.
Shams al-Dîn Ibn Qudâmah writes in al-Sharh al-Kabîr (3/203): “The navel and the knees themselves are not part of the `awrah. This is the opinion of Mâlik and al-Shafi`î. Abu Hanîfah says that the knees are part of the `awrah.”
It is preferable for a man to cover his shoulders while in prayer.
The Prophet (peace be upon him) said: “None of you should pray in a single garment without having part of it upon his shoulder.” [Sahîh al-Bukhârî (359) and Sahîh Muslim (516)]
The majority of scholars are of the opinion, however, that covering the shoulders is not obligatory.
Al-Nawawî explains this in his commentary on the hadîth [Sharh Sahîh Muslim (4/231-232)]:
Scholars have explained that the wisdom behind doing so is that if the worshipper is wearing a waistcloth without having part of it upon his shoulder, he cannot be secure that his `awrah will not become exposed as opposed to if he places part of it upon his shoulder.
Also, he might have to hold it (his waistcloth) with one or both of his hands and in doing so neglect, among other things, the Sunnah of placing his right hand over his left hand beneath his chest and that of raising his hands when he is supposed to raise them.
It is also because he is neglecting to cover his upper body, and this is a place for beautiful apparel. Allah says: “And wear your beautiful apparel at every time and place of prayer.” [Sûrah al-A`râf: 31]
Mâlik, Abû Hanîfah, al-Shâfi`î, and the majority of scholars consider the prohibition here to be one of dislike and not one of unlawfulness. Therefore, if a man prays in a single garment that covers his `awrah without placing any of it upon his shoulder, his prayer will be valid, though his action will be disliked.
The official position in the Hanbalî school of thought is that it is obligatory for a man to place part of the garment upon his shoulder if he is able to do so. Shams al-Dîn Ibn Qudâmah writes in al-Sharh al-Kabîr (3/203):
Whenever a man covers his `awrah in prayer, his prayer will be acceptable, as long as he has something of clothing upon his shoulder, regardless of whether it is from the garment that is covering his `awrah or something else. This is if he is able to do so.
However, the strongest opinion is that it is not obligatory. Sheikh `Abd al-`Azîz b. Bâz says: “It is obligatory for every Muslim to cover his `awrah while praying. The `awrah for men is from the navel to the knee. As long as this area is thoroughly covered, prayer will be valid.”
And Allah knows best.
Source: Islam Today