It is to be stated first that covering the head in prayer is not a Sunnah and there is no Hadith of the Prophet recommending it.
Shedding more light on this is the following fatwa: “A man does not need to cover his head for prayer. The Prophet, peace and blessings be upon him, never hinted for that. On the contrary, we see that he once made Ghusl and came to lead the prayer whereas his head was dripping. That means he was not covering his head. In Ihram, a man is not allowed to cover his head. Covering the head in prayer is not a matter of Deen, but it is cultural or traditional.”
We’d like also to cite the following: “There is no Hadith which requires or recommends Muslim men to cover their heads when they offer their prayers, whether obligatory or voluntary. It should be remembered that the Prophet and his Companions used to cover their heads when they were in the mosque or in the marketplace or indeed anywhere else. So did the rest of the Arabs. In other words, this was the customary dress in Arabia which continued after Islam. [Certain headgears are linked to specific areas. Arabs, Indonesians, Nepalese, Russians, Pakistanis, Moroccans, etc. can be linked to their origin with their headgears.] As such, wearing a cap or covering one’s head by a man for prayers is neither recommended nor obligatory.
It is certainly not a Sunnah. Does it mean that every Muslim has to wear a head covering at all times? Wearing a head covering was traditional in Arabian society at the time of the Prophet. He would have pointed out that it is recommended or obligatory in prayer if it was so. The fact that he did not tell us that means that he only had his head covering as part of his traditional dress. If someone wears a head covering in prayer in order to follow the example of the Prophet, he is rewarded simply for his intention. However, since the Prophet has not pointed out anything regarding this particular matter, we cannot say that it is recommended.” [Source: www.islamicity.com]
In this regard, Sheikh `Atiyyah Saqr, former head of Al-Azhar Fatwa Committee, states:
“There is no Hadith to support the covering of the head at prayers, so it is judged according to the prevailing conventions. If it is a common habit for men to wear a head cover in ordinary conditions, then they can wear it while performing prayer, as there is no textual evidence commending or prohibiting it. On the other hand, if it is the common custom for men to uncover their heads, then there is nothing wrong in uncovering it during prayer, because what is agreed upon by entire Muslims to be right, then it is deemed so by Allah.
Ibn `Asakir reported on the authority of Ibn `Abbas, may Allah be pleased with him, that the Prophet, peace and blessings be upon him, sometimes took off his turban and put it before him while performing prayer as a barrier to prevent others from passing before him.
The Hanafi jurists view that there is nothing wrong in uncovering the head while praying and that it is even deemed recommendable if it is done for the sake of maintaining Khushu` (concentration at prayer).”