Is it permissible for me to combine the Fajr and Dhuhr prayers and perform them after finishing work?

It is not permissible to delay prayer beyond its prescribed time, except for a legitimate Shar'i excuse, such as forgetfulness or sleep. Worldly matters are not considered an excuse for delaying prayer, for sincere believers are not distracted by trade from the remembrance of Allah and the establishment of prayer. Prayer is "a scripture decreed at appointed times," enjoined at its specific time. Delaying it without a valid excuse incurs divine warning, as stated in His Almighty saying: "There succeeded them later generations who neglected prayers and pursued desires; so they are going to meet evil," and His saying: "So woe to those who pray, [but] who are heedless of their prayer." Therefore, prayer must be performed on time, and if work prevents this, one must leave it and seek another job that does not conflict with performing prayer.