Has there been a consensus (Ijma') that the purity of clothes, water, and body is a condition for the validity of prayer (Salah)? If so, what type of consensus is it, is it permissible to oppose it, and what is the ruling on one who opposes it?

Ibn Abd al-Barr's intent regarding the consensus on removing impurity is its obligatoriness, not its being a condition. Thus, the prayer of one who prayed with impurity out of forgetfulness or heedlessness is valid. This aligns with the view of the Malikis and Al-Shawkani, who hold that removing impurity is obligatory, but the prayer is valid if impurity is present, because its removal is an obligation and not a condition. There is no consensus that purity from impurity is a condition for the validity of prayer; rather, it is the opinion of the majority. Therefore, if someone imitates Al-Shawkani in this matter, being unable to weigh the evidences, or if a student of knowledge exerted effort and preferred this view, there is no harm in it.