Should he pray behind someone who says that it is not obligatory for women to cover their hair?

Praise be to Allah.

Firstly: 

What this man says about America being more of a land of Islam than the land of the two sacred mosques is false, and there is no need to produce evidence that it is false, because there is no wise man, let alone any scholar, who would say that America is a land of Islam, and America itself makes no such claim. 

Secondly: 

It is obligatory for women to cover their heads according to scholarly consensus, based on a great deal of evidence which includes the command to observe hijab, the clearest of which is the words of Allaah, may He be exalted (interpretation of the meaning): 

“O Prophet! Tell your wives and your daughters and the women of the believers to draw their cloaks (veils) all over their bodies (i.e. screen themselves completely except the eyes or one eye to see the way). That will be better, that they should be known (as free respectable women) so as not to be annoyed. And Allaah is Ever Oft‑Forgiving, Most Merciful”

[al-Ahzaab 33:59]

This indicates that it is obligatory to cover the face too, because the jilbab is lowered from the top of the head until it covers the face and chest. 

We have explained the evidence for it being obligatory to cover the face in the answer to question no. 11774, and this evidence applies even more so to covering the head. 

The scholars differed with regard to covering the face, but they did not differ concerning the fact that it is obligatory for a woman to cover her head and hair in front of non-mahram men. 

Imam Abu Bakr al-Jassaas said in his tafseer, Ahkaam al-Qur’aan (3/485), commenting on the verse (interpretation of the meaning): “And as for women past childbearing who do not expect wedlock, it is no sin on them if they discard their (outer) clothing in such a way as not to show their adornment. But to refrain (i.e. not to discard their outer clothing) is better for them. And Allaah is All‑Hearer, All‑Knower” [al-Noor 24:60]:

There is no dispute that the hair of an old woman is ‘awrah and it is not permissible for a non-mahram man to look at it, just as in the case of a young woman. If she prays bareheaded, then her prayer is invalid, just as in the case of a young woman. End quote. 

It should be said to this pseudo-scholar and his ilk: This hijab or modesty that you speak of: what is the evidence for it, what are its limits, where does Allaah mention it in His Book or His Messenger (peace and blessings of Allaah be upon him) in his Sunnah? If he mentions the verses of hijab, he should be asked to study their tafseer. If he ignores the verses of hijab, they should be mentioned to him, “so that those who were to be destroyed (for their rejecting the Faith) might be destroyed after a clear evidence, and those who were to live (i.e. believers) might live after a clear evidence” [al-Anfaal 8:42].

 Thirdly: 

What the Muslims should do is respect the Qur’aan and Sunnah, and adhere to the limits set by them, strive to learn their rulings and not accept whatever any charlatan says, especially in these times when there are so many who have the audacity to interpret sharee’ah according to their whims and speak without guidance.  

Our Muslim sisters have to fear Allaah. Let their example be ‘Aa’ishah, Faatimah, Khadeejah and the first generation of righteous Sahaabi women who hastened to cover their entire bodies when the verses of hijab were revealed, and when they went out they could not be recognized because of the black garments they wore, and their faces could not be seen, let alone their hair. 

Fourthly: 

This speaker should be advised and told of the rulings on hijab and its nature from the Qur’aan and Sunnah, and the teachings of the scholars. If he responds, then praise be to Allaah, and this is what we hope for him. If he persists in his attitude, then he should not be allowed to teach or exhort the Muslims. He should not be allowed to lead the Muslims in prayer and they should not pray behind him, rather he should be shunned and forsaken until he comes back to the truth. 

We ask Allaah, may He be glorified, to guide the misguided Muslims, and to make us steadfast in following His religion until we meet Him.  

And Allaah knows best.