What Happens If You Deliberately Pray without Wudu?
Question

I know that it's not allowed to pray if you have "Janabet" Now if someone have prayed with "Janabet" then what is the ruling of Islam on him. Let me make the situation a little more clear. This person's age was 20~21. And he went with his dad to mosque, over there his father "Ordered" him to conduct Jamat (Nimaz). Now in this situation the guy was not able to tell his dad that he is in "Janabet" and needs Ghusl, so he did the "Wudu" and conducted the jamat. Now from inside, he is totally broken, and worried about his SIN, he read in one book that if you conduct "Salat" without Wudu, then you are OUT OF ISLAM !!! .... Now in this situation what does he have to do ? Is he Out of ISLAM or NOT ? How he can overcome of his this SIM ... and do TOWBA ? Do he need to do his EMAN's TAJDEED ? I will be looking forward to hearing from your side, a detailed answer. I know that you have said that you ask only related to Ramadan questions, but I have discovered your site now. So I hope that when u will have time then u will reply to this IMPORTANT question. My friend is really in Mental Trouble due to what happened.
Praise be to Allah.What happens if you deliberately pray without Wudu?
It is well known and no Muslim has any excuse for not knowing that purification from impurity, whether minor or major, is obligatory and is a condition of prayer being valid. Whoever prays without purifying himself , whether deliberately or by mistake, his prayer is invalid and he has to repeat it; if it is done deliberately then he has committed a major sin. 
Shaykh Al-Islam Ibn Taymiyah (may Allah have mercy on him) said: 
“The Muslim should not pray facing any direction other than the Qiblah, or without doing Wudu , bowing and prostrating. Whoever does that deserves to be rebuked and punished.” (Minhaj As-Sunnah An-Nabawiyyah, 5/204 )
There is a stern warning issued to one who does that. It was narrated from `Abdullah ibn Mas`ud (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: “It was ordered that one of the slaves of Allah be flogged in his grave with one hundred lashes, but he kept asking until it was reduced to a single blow. So he was given a single blow, then his grave was filled with fire. When he came round, he said: `Why did you flog me?` It was said to him: `You offered one prayer without being in a state of purity , and you passed by one who was being wronged and did not help him.`” (Narrated by At-Tahawi in Mushkil Al-Athar, 4/231; classed as sound by Al-Albani in As-Silsilah As-Sahihah, 2774) 
Does praying without Wudu take one out of Islam?
The scholars agreed that whoever prays without being in a state of purity because he believes that it is permissible or out of disrespect is a disbeliever. He should be asked to repent, and if he repents, all well and good, otherwise he should be executed. 
But if he prays without Wudu out of negligence, not because he thinks it is permissible or out of disrespect, Imam Abu Hanifah (may Allah have mercy on him) is of the view that this is also disbelief. However, the majority of scholars are of the view that he is not a disbeliever, rather he has committed a major sin. 
An-Nawawi (may Allah have mercy on him) said:  
“If he knows that he is impure and that it is prohibited to pray when one is impure , then he has committed a grave sin, but he does not become a disbeliever thereby in our view, unless he regards that as permissible. But Abu Hanifah said: He has committed disbelief because of his disrespect. 
Our evidence is that it is a sin so it is akin to zina and the like.” (Al-Majmu` (2/84); Rawdat At-Talibin, 10/67)
(See the Hanafi view in Al-Bahr Ar-Ra`iq, 1/302, 151; 5/132; Hashiyat Ibn `Abidin, 3/719)
The one who has prayed without purifying himself has to repent and seek forgiveness, and resolve not to do such a thing again, then he should repeat the prayer that he offered without purifying himself. Allah accepts the repentance of those who repent to Him. And he does not have to enter Islam anew. 
And Allah knows best.