He interrupted Tawaf in order to go and relieve himself, then he came back and completed it. Is his Tawaf valid?

Being in a state of purity is an essential condition of tawaf being valid, according to the majority of scholars. But they differed with regard to the case where a person becomes in a state of minor impurity during tawaf, then he goes and does wudu: should he complete the circuits or start tawaf all over again? There are two views: 

The Hanafis and Shaafa‘is are of the view that he may complete his tawaf, even if there was an interval in between, because doing the circuits consecutively is not a condition required in tawaf. 

The Maalikis and Hanbalis are of the view that he should start tawaf all over again, because minor impurity (when a person breaks his wudu during tawaf) renders tawaf invalid. So he has to start all over again. The same ruling applies if the interruption between circuits is lengthy, because doing the circuits consecutively is one of the conditions of tawaf being valid. 

See: al-Mawsoo‘ah al-Fiqhiyyah (29/131) 

Shaykh ‘Abd al-‘Azeez ibn Baz (may Allah have mercy on him) said:

If a person becomes in a state of minor impurity during tawaf, his tawaf is rendered invalid, as in the case of prayer. So he should go and purify himself, then start tawaf all over again. This is the correct view. There is a difference of scholarly opinion concerning this matter, but this is the correct view with regard to both tawaf and prayer, because the Prophet (blessings and peace of Allah be upon him) said: If one of you breaks wind whilst praying, let him go and do wudu, and repeat his prayer.” Narrated by Abu Dawood; classed as saheeh by Ibn Khuzaymah. And tawaf is of the same nature as prayer in general. 

End quote from Majmoo‘ Fatawa ash-Shaykh Ibn Baz (10/160). 

Shaykh Muhammad ibn ‘Uthaymeen (may Allah have mercy on him) said: 

With regard to tawaf and sa‘i, it is stipulated that the circuits be done consecutively, and if there is a lengthy interruption between them, the first circuits are rendered invalid, and the individual must start tawaf all over again. But if the interruption is not lengthy, such as if he sits down for two or three minutes, then gets up again and completes it, there is nothing wrong with that. 

End quote from Majmoo‘ Fatawa ash-Shaykh Ibn ‘Uthaymeen (22/293) 

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: 

A man did tawaf al-ifaadah, and during the tawaf he became in a state of minor impurity, so he went and did wudu, then he came back and completed his tawaf without starting all over again, thinking that this was a valid action. What must he do now? 

He replied:

With regard to the tawaf in which he became in a state of minor impurity, then he went and did wudu, if we say that being in a state of purity is a condition of tawaf being valid, then the tawaf in which he became in a state of minor impurity was rendered invalid, so basing the latter part of it on the first part is not valid. Based on that, he is now regarded as not having done tawaf al-ifaadah. 

But if we say that wudu is not a condition of tawaf being valid, then we should see whether his looking for water and doing wudu took a long time. In that case, his tawaf is not valid either, because doing the circuits consecutively is a condition of tawaf being valid. But if he found water nearby, then did wudu and came back quickly, then his tawaf is valid. 

End quote from Majmoo‘ Fatawa wa Rasaa’il al-‘Uthameen (22/357) 

Usually going to the washrooms during Hajj season, when the place is very crowded, then doing wudu, takes a long time, which interrupts the continuity between the circuits, so it is not valid to complete tawaf based on the previous circuits. 

Based on that: 

If you have not repeated tawaf al-ifaadah up till now, then your Hajj is not complete and you have to go back to Makkah and do tawaf al-ifaadah, because tawaf al-ifaadah is one of the pillars or essential parts of Hajj that must be done – unless you did this based on a fatwa from one of the scholars, or following a scholar who said that. In that case you do not have to do anything further. 

For more information, please see fatwa no. 49012 

And Allah knows best.