Is it permissible to criticize rulers according to Ahl al-Sunnah, or is silence obligatory?

The methodology of the People of the Sunnah (definition) is to advise rulers with gentleness, kindness, and good manners, for this is what the wise Shari'ah has commanded. The advice should be in private, not in public. So, whoever wishes to advise a ruler should not do so openly, but rather take him by the hand and be alone with him. Advice to the Muslim leaders involves assisting them in truth, obeying them in it, enjoining them to it, reminding them gently, refraining from rebelling against them, and uniting the hearts of the people in obedience to them. It is a door among the doors of changing evil, and it has manners and controls that achieve the legitimate benefit. One should not confuse it with criticism, which is among the doors of discord, spreading corruption and chaos. Whoever is able to offer advice should not remain silent.