How, in light of the Qur'an and Sunnah, can one deal with a manager who lies and deceives at work, and how can his true nature be exposed through supplication (du'a) and lawful cunning, especially after his actions have negatively affected the employee's relationship with the executive director and his health?

The best solution is to deal kindly and patiently with the manager's mistakes, such as lying, deception, and his spoiling the relationship between you and the executive manager. Allah Almighty said: "Repel evil with that which is best, and behold, he between whom and you was enmity will become as though he was a devoted friend. But none is granted it except those who are patient, and none is granted it except one having a great portion [of good]."

Furthermore, it is necessary to avoid describing the manager with terms that are offensive, as they include forbidden backbiting.

If you do not wish to act upon the aforementioned advice, it is permissible to supplicate against the oppressor, with conditions mentioned in previous fatwas.