People of wisdom state:
Anyone who does not observe (Islamic manners called) aadaab cannot win Allahu ta'ala's love and pleasure. Nor can he become His dear slave. The path of Islamic superiors, from beginning to end, is built upon manners. Knowledge is not learned before manners are learned. Good manners are the source of fayd (spiritual power that flows from heart to heart and helps one obey Allahu ta'ala's commandments) because fayd flow to a well-mannered person, not an ill-mannered one. Islam is good manners and modesty. Good manners are the gateway, and modesty comes after them. Besides, morals and manners are external manifestations of wisdom because one's level of wisdom is directly proportional to one's firmness in practicing Islamic manners and etiquette. Adab (sing. of aadaab) means considering oneself imperfect and knowing one's place. In fact, the highest knowledge is to know one's place.
Three kinds of manners to be observed
1. There are manners to be observed toward Allahu ta'ala. That is, one must be a servant to Him both inwardly and outwardly, performing all of His commandments and abstaining from all of His prohibitions.
2. There are manners to be observed toward our Master the Messenger of Allah. One must follow him in belief, actions, and manners.
3. There are also manners to be observed toward one's spiritual guide because the guide has acted as an intermediary for one to obey our Master the Prophet. Therefore, one should never ever forget his master.
Allahu ta'ala forgives the sins and wrongdoings committed against Himself when repentance is made. However, He does not forgive those that are committed against His Beloved (our Prophet). He is jalis-i ilahi. That is, he is with Allahu ta'ala. So is the case with other Islamic superiors, like Hadrat Imam-i Rabbani, who are our Prophet's inheritors. Upsetting them, therefore, causes disastrous consequences, so one must strictly avoid it. Notable Islamic figures stated, "I benefited from my spiritual guide thanks to my good manners alone."
Once upon a time, while a teacher named Mullah 'Abdullah, together with his two students, was traveling to Nehri (a village in Hakkari, Turkey) to visit Hadrat Sayyid Taha al-Hakkari, one of the superiors of the Silsila-i 'Aliyya, they sat by a brook. Mullah 'Abdullah said to his students, "Because a great person lives in Nehri, everybody goes there by performing an ablution. I will break this custom and go there without an ablution." Though his students tried to convince him, saying, "Sir, let us not break this custom. Let us go there by performing an ablution," Mullah 'Abdullah replied, "Is it an Islamic commandment? I will not do it." Some time later, while he was washing his hands and face to cool himself off, his staff fell into the water. At the time he stretched out his hand to take it, the staff hit him on the head and in the face, leaving his face and eyes covered in blood. Then the staff disappeared. Thereupon, he deeply regretted uttering those words. Having bandaged his injured parts, he made an ablution and went to Nehri. When he entered the convent of Hadrat Sayyid Taha, he saw that that staff was hung on the wall. As his eyes were fixed on the staff, Hadrat Sayyid Taha stated, "What is the matter? Are you looking at this staff because it beat you?" Filled with remorse, Mullah 'Abdullah repented of what he had done and was honored with becoming a student of his.