His wife does not pray regularly
Question

                I am a religiously-committed young man. I married a woman about six years ago and I have a son and daughter from her. Before marriage, she was described to me as religiously-committed, then after that I found out that she does not pray regularly and when I ask her whether she prayed or not, she tells me that she prayed, but I am certain that sometimes she did not pray (i.e., I checked on her between prayers). I have offered her a great deal of advice and I have spoken to her frankly on some occasions and by means of hints on others. What I cannot do is forsake her in her bed, because I cannot do without marital relations. I divorced her once, then I took her back because I feared for our children if the family broke up. I have prayed to Allaah for her a great deal, asking Him to guide her. What should I do with her? Should I put up with her (knowing that I do not find fault with her for anything except this)? If I put up with her, what should I do? Will I be sinning if I am intimate with her? Or what should I do?.
Praise be to Allah.What the husband should do 
    is enjoin good upon his wife and forbid her to do that which is evil. He 
    should call her to do good and warn her against evil, thus fulfilling the 
    responsibility that Allaah has given him. Allaah says (interpretation of the 
    meaning): 
“O you who believe! Ward 
    off yourselves and your families against a Fire (Hell) whose fuel is men and 
    stones”
[al-Tahreem 66:6]
And the Prophet  (peace 
    and blessings of Allaah be upon him) said: “A man is the shepherd of his 
    household and is responsible for his flock.” Narrated by al-Bukhaari (893) 
    and Muslim (182).  
One of the greatest of good 
    deeds is performing prayer on time as enjoined by Allaah, and one of the 
    greatest of bad deeds is being careless and negligent about that, by not 
    praying at all, or by not praying on time. Allaah criticized the one who 
    does that, as He says (interpretation of the meaning): 
“Then, there has 
    succeeded them a posterity who have given up As‑Salaah (the prayers) [i.e. 
    made their Salaah (prayers) to be lost, either by not offering them or by 
    not offering them perfectly or by not offering them in their proper fixed 
    times] and have followed lusts. So they will be thrown in Hell”
[Maryam 19:59]. 
     
And the Prophet  (peace 
    and blessings of Allaah be upon him) said: “Between a man and shirk and kufr 
    there stands his giving up prayer.” Narrated by Muslim (82). 
And he  (peace and 
    blessings of Allaah be upon him) said: “The one who does not pray ‘Asr, his 
    good deeds are fruitless.” Narrated by al-Bukhaari (553). 
If your wife does not pray 
    at all, then there are ahaadeeth from the Prophet  (peace and blessings 
    of Allaah be upon him) which show that not praying at all is kufr, and it is 
    not permissible for you to keep her because she is not a Muslim. In that 
    case you have to tell her that her insisting on not praying means that she 
    is not your wife, so she must either repent and start to pray regularly, or 
    else you must leave her. 
But if she prays sometimes 
    and not at others – which seems to be the case from your question – then 
    that does not put her beyond the pale of Islam, but you have to advise her 
    and look for the causes of her shortcoming so that they can be dealt with. 
    But that should be done in a kind and gentle manner. So explain to her the 
    importance of prayer, and the sin involved in falling short with regard to 
    it. Strive to strengthen her faith and encourage her to do good deeds and 
    acts of worship. Help her to make friends with some righteous women and 
    supply her with some useful books and tapes that will encourage her to do 
    good, and always ask her about her prayers. 
We ask Allaah to guide you 
    both to that which is good. 
See also question no. 
    12828. 
And Allaah knows best.