What is the ruling on one who habitually prays Fajr after its time has expired, before going to work, despite knowing that this is wrong, and is this considered an act of disbelief (kufr)?

There is no doubt that intentionally performing the prayer after its prescribed time is a grave sin, and some scholars have even gone so far as to consider the perpetrator a disbeliever. The questioner should continue to advise the negligent person regarding the Fajr prayer with gentleness, kindness, and wisdom, focusing on offering sincere advice rather than declaring someone a disbeliever.