It is narrated from Imam Sadeq (AS) who said: The government officials and rulers are not allowed to fail in three acts.
1.Guard and protect the borders of the country against the threats from enemies.
2.Selecting pious believers to fill the official posts.
3.Take care of the oppressed people and attend to their cases of oppression
[1] Tohaful Oqool, Page 333.
Source: en.shafaqna.com