Praise be to Allah.
Domesticated animals are of two types, the first of which is those whose flesh may be eaten, such as sheep, goats and deer. The urine and faeces of this type are pure (tahir). Ibn Qudamah (may Allah have mercy on him) said in al-Mughni (2/492):
The urine and faeces of animals whose flesh may be eaten are pure… Malik said: The scholars do not regard the urine of animals whose flesh may be eaten and whose milk may be drunk as impure (najis). End quote.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
Regarding the urine and faeces of animals whose flesh may be eaten, most of the early generations were of the view that it is not impure. This is the view of Malik, Ahmad and others. It may be said that none of the Companions suggested that it is impure; rather the view that it is impure came later, and no such view was held by the Companions.
The second type of domesticated animals is those whose flesh may not be eaten, such as cats. The urine and faeces of this type is impure, and the individual must cleanse and purify himself if it gets onto his clothes or body.
An-Nawawi (may Allah have mercy on him) said in al-Majmu‘ (2/548):
Regarding the urine of all other animals whose flesh may not be eaten, it is impure in our view and in the view of Malik, Abu Hanifah, Ahmad and all the scholars. End quote.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
With regard to the faeces of animals whose flesh may not be eaten, such as mules and donkeys, it is impure according to the majority of scholars."(Majmu‘ al-Fatawa 21/74).
See also the answer to question no. 111786 .
If the animal is one whose flesh may not be eaten, and it appears to be clean and pure, then it cannot be deemed to be impure on the basis of uncertainty; rather that can only be decided on the basis of certainty.
The scholars of the Permanent Committee for Ifta’ were asked:
If a person gets up after sleeping, purifies himself and prays, then he goes back to his bed to sleep some more, and finds something on his bed that gives cause for thinking that he may have urinated in his bed, what should he do when he has already prayed in the clothes he was wearing but this is mere uncertainty?
They replied:
The basic principle is that he is in a state of purity, and passing doubt or uncertainty carries no weight. End quote.
Fatawa al-Lajnah ad-Da’imah (5/282-283). They were also asked:
If the Muslim is not sure whether one of his garments is impure, but he does not see any trace of impurity on the garment, what is the ruling that case?
They replied: If he is certain that one of his garments was pure, and is not certain that it has become impure, then it remains as it was, and is still to be deemed as pure. What is certain cannot be cancelled by what is uncertain."(Fatawa al-Lajnah ad-Da’imah 6/67-68).
For more information, please see the answer the question no. 10949 .
Based on that, it is permissible to pray in the clothes that you were wearing when you were holding that pet or domesticated animal, if it is one whose flesh may be eaten, regardless of whether its urine (or faeces) got onto you or not, because its urine and faeces are pure, as noted above.
But if the animal is one whose flesh may not be eaten, such as a cat, it may also be regarded as pure, unless the Muslim becomes certain that it [the garment] has become impure, in which case he must wash away that impurity before starting to pray.
We should point out that it is haram to keep dogs unless they are needed for hunting or guarding.
For more information on the purity and impurity of animals, please see the answer to question no. 146155 .
And Allah knows best.
Comment