Is it permissible for a Muslim to pray sometimes according to the Shafi'i method, and at other times according to the Hanafi, Maliki, or Hanbali methods?

The differences among the madhhabs (schools of thought) regarding some actions in prayer are due to two reasons:

1. Diversity of established descriptions from the Prophet, peace and blessings be upon him: Examples include the tashahhud (testification of faith) and the istiftah (opening supplication), which have been reported in more than one manner. It is prescribed for a Muslim to perform any of these manners with the intention of following the Sunnah.

2. Differences among scholars in understanding texts and deriving rulings: In these matters, the truth is one and does not multiply. A Muslim must strive to know the ruling of Allah and His Messenger to the best of their ability. If one is not among those capable of ijtihad (independent reasoning), they may follow a scholar in whose knowledge and piety they trust. It is not permissible for someone who has committed to a madhhab to switch to another madhhab without a legitimate reason or excuse, unless it becomes clear to them what necessitates preferring one opinion over another based on evidence or because one scholar is more knowledgeable and pious.

A Muslim must act according to what the evidence from the Qur'an and Sunnah indicates, and it is not permissible for them to switch between madhhabs merely according to their whims.