What is the ruling regarding someone who shortens the prayer (qasr) during the first four days of a journey where they intended to stay longer than that, and then completes the prayers (itmam) for the remaining days, and has any scholar held this opinion?

The majority of scholars hold that if a traveler intends to stay in a place for more than four days, he must perform the prayer in full from the first day of his arrival, and it is not permissible for him to shorten it. This is the view of the Maliki, Shafi'i, and Hanbali schools, and it is what Ibn Baz ruled. Therefore, whoever shortened the prayer in the first few days, thinking it was permissible for him, his action is not valid, and he must repeat those prayers as a precautionary measure, even though some scholars are of the opinion that repetition is not obligatory for someone who erred out of ignorance.