Will an employee be held accountable for lying to obtain an emergency leave, given his fear that his lie might affect his sick mother, and is his leave permissible despite his colleagues being absent with invalid excuses, and will he be sinful for cursing clients to himself as a way to vent his anger?

The questioner is thanked for his sincerity in work, but lying to the manager to obtain a leave is impermissible, incurs sin, and necessitates seeking forgiveness. It is also required to return the salary taken unjustly or to rectify the situation. The Hadith (definition) "Do not feign illness" is weak, and even if it were authentic, its intent is about feigning illness by the person himself, not lying to him. As for cursing people inwardly without uttering it, there is no sin in it, but one should strive against oneself to abandon it.