1. The First: Sincerely directing all worship to Allaah alone.
2. The Second: Holding fast to the Jama'ah, and hearing and obeying [the Muslim Rulers].
3. The Third: Being extremely cautious of innovation (bid'ah) and the people of religious innovation.
From the evidences that provide textual support for these fundamental principles is the following:
Al-'Irbaad Ibn Saariyah, radiAllaahu 'anhu, said, "The Messenger of Allaah, sallAllaahu 'alayhi wa sallam, admonished us one day after the early morning prayer. The admonition was heartfelt and eloquent and caused the eyes to shed tears and the hearts to tremble. A man from amongst us said, 'Certainly, it is as if this is a farewell admonition, so with what do you advise us, O Messenger of Allaah, sallAllaahu 'alayhi wa salam,? He replied, 'I advise you to fear Allaah and to listen and obey those in authority over you even if it were an Abyssinian slave. Indeed, whoever from amongst you lives long will witness much differing. And beware of newly invented matters for surely they are misguidance. Whoever from amongst you lives to witness this, then cling to my Sunnah and the way of the rightly guided Khulafaa [Caliphs] who will come after me and grab hold of it with your molar teeth.'"
Suhayl Ibn Abi Saalih said upon the authority of his father who narrated from Aboo Hurayrah, radiAllaahu 'anhu, that the Messenger of Allaah, sallAllaahu 'alayhi wa salam, said "Indeed, Allaah loves for you three things and despises you for three things. He loves for you that you worship Him alone and that you do not associate any partners with Him; that you hold on to the rope of Allaah altogether; and that you advise those who have been placed in authority over you. Allaah despises for you gossip, the wasting of wealth, and incessant questioning." [Muslim, Ahmad]
These three principles have been explicitly mentioned in the narration of Zayd ibn Thaabit, radiAllaahu 'anhu, who said, "I heard the Messenger of Allaah, sallAllaahu 'alayhi wa salam, say, 'Allaah will brighten the face of the one who hears from us a hadeeth (narration), memorizes it and then coveys it to others. Perhaps, the one who conveys it does not comprehend it, and perhaps the one carrying fiqh conveys it to one who has more understanding than himself. There are three characteristics which when present the heart of a Muslim will never harbor any vindictive feelings; Sincerely performing an action for Allaah, advising those who have been places in authority over you and holding fast to the Jama'ah. Indeed their call protects all those behind them."
These three characteristics encompass everything that the people's Religion and their worldly affairs are built upon. Shaykhul-Islaam Muhammad Ibn 'Abdul-Wahhaab (d.1206H) said, "There is no deficiency in a person's Religion or worldly affairs except due to a discrepancy in these three things or some of them." [Masa'il al-Jahiliyyah]
Shaykh Saalih al-Fawzaan, hafidhUllaah