The Forty Hadiths of al-Nawawi
On the authority of the Mother of the Believers, Umm 'Abdullah 'A'ishah, may Allah be pleased with her, who said:
The Messenger of Allah, peace and blessings of Allah be upon him, said:
"Whoever introduces into this matter of ours that which is not part of it, it is rejected."
Narrated by al-Bukhari and Muslim.
And in a narration by Muslim:
"Whoever performs an act that is not in accordance with our matter,"
"it is rejected."
This hadith clarifies a fundamental principle among the foundations of Islam,
which is the obligation to follow the Sunnah of the Prophet, peace be upon him,
and to abandon innovations in the religion.
For every act of worship or deed by which one seeks to draw near to Allah,
if it is not in accordance with the Qur'an and the Sunnah,
it is rejected by the one who performed it,
no matter how sincere his intention may be.
The hadith teaches the Muslim that valid worship
is established upon sincerity to Allah
and following the Messenger of Allah, peace be upon him.
Thus, the rectitude of a deed is not achieved by intention alone,
but by its conformity to the guidance of the Prophet, peace be upon him.