The issue of sticking to a madhhab has in it some detail. If a person has the ability to know the ruling from its proof, and to deduce the ruling from its proof, then it is not permitted for him to cling to a madhhab. rather, it is upon him to take the ruling from the evidence - if he has the ability to do so. However, this is rare amongst the people, since this is a quality of the mujtahideen from the people of knowledge; those that have reaced the levels of ijtihaad. As for one who is not like that, then he cannot take the rulings directly from the evidences. And this is the predominant case amongst the people, especially in these latter times. So [in such a case] there is no harm in adopting one of the four madhhabs and making taqleed of one of them. However, he should not make blind taqleed such that he takes all that is in the madhhab; whether it is correct or incorrect. Rather, it is upon him to take from the madhhab that which - in his view - does not clearly oppose the evidence. As for those views in the madhhab which clearly oppose the evidence, then it is not permissible for the Muslim to take it. Rather it is upon him to adopt what is established by the proof, even if it is in another madhhab So his leaving the madhhab for another madhhab in order to follow the evidence is something good; this is a matter which is good - rather it is obligatory;since following the evidence is an madhhab in order to follow the evidence is something good; this is a matter which is good - rather it is obligatory;since following the evidence is an obligation.
As for adopting one madhhab sometimes and another at other times, then this moving is from the angle of following ones desires and seeking concessions, and this is not permissible. Meaning, that whatever accords with ones whims and desires, from the sayings of the people of knowledge, is taken - even if it opposes the proof; and whatever opposes ones whims and desires is left - even if it has a proof. This is the following of whims and desires, and we seek refuge in Allaah [from that]. Thus, moving from one madhhab to another, due to following ones desires, or due to ease or seeking concession; then this is not permissible. As for moving from one madhhab to another due to following an evidence, or to flee from a saying that does not have a proof, or from an erroneous view - then this is a matter that is encouraged and sought from a Muslim. And Allaah knows best.
As for the issue concerning the differences between the four madhhabs in the Prayer, then the four madhhabs - and all praise is for Allaah - are in Prayer, then the four madhhabs - and all praise is for Allaah - are in agreement about most of the rulings concerning the Prayer, in general. Their differences are in some of the details of the Prayer. From [such differences] are, for example, that [one of them] may consider something to be prescribed, whilst another may not consider it to be prescribed; one may consider something to be obligatory, whilst another may consider it to be recommended; and so on. So the differences are in the details of the Prayer. But as for the rulings of the Prayer in general, then there is no difference - and all praise is for Allaah