Solāh is not acceptable Without Valid Wudhu’
A question was asked: sometimes after Solāh I remember that I had not gone through without 'wudhu'. What is the ruling? Should I do my wudhu’ and pray again?
In the name of Allāh, the Most Gracious, the Most Merciful;
All the praise and thanks is due to Allāh, the Lord of al-'ālamīn. There is none worthy of worship except Allāh, and that Muhammad, Sallallāhu alayhi wasallam, is His Messenger.
If one remember that he had gone through Solāh without 'wudhu' would have to take the wudhu’ and repeat the Solah. The scholars are unanimously agreed on that, because purity (Taharah) being one of the conditions of Solāh to be valid. The evidence for that are the words of Rasūlullāh (Sallallāhu `alayhi wasallam):
“Allāh does not accept the Solāh of any of you if he breaks his wudhu’, unless he does wudhu’ again.”
[This is narrated by al-Bukhaari, 6954; Muslim, 225.]
`Abdullah Ibn ‘Umar (radiyallāhu`anhu) said: I heard the Messenger of Allah (Sallallāhu `alayhi wasallam) say: “No Solāh is accepted without purification.”
[Narrated by Muslim (224)]
Al-Nawawi (rahimahullāh) said:
The Muslims scholars are unanimously agreed that it is haram for a person who has broken his wudu’ to perform Solāh, and they are unanimously agreed that his prayer is not valid, whether he is aware that he broke his wudhu’ or is unaware of that or forgot. But if he performed Solāh because he was unaware of it or forgot, then there is no sin on him, but if he was aware that he had broken his wudhu’ and that it was harām for him to pray in this situation, then he has committed a grave sin.
This is in contrast to the person who has some impurity (najasah) on his clothes and he forgets it. He does not have to repeat his prayer because Jibril came to the Prophet (Sallallāhu `alayhi wasallam) whilst he was praying, and told him that there was something dirty on his shoes. He took them off and continued praying. This was narrated by Ahmad from the hadith of Abu Sa’id al-Khudri (radiyallāhu`anhu) in his Musnad. This hadith proves that the one who is unaware of the najasah does not have to repeat his Solāh, and this applies also to the one who forgets that there is some najasah present.
And Allah knows best.
[See: I’lam al-Musafirin bi Ba’d Adab wa Ahkam al-Safar wa ma yakhuss al-Mallahin al-Jawwiyyeen by Shaikh Muhammad ibn Salih al-‘Uthaymeen, p. 12]
[Via Islam Q&A]