“And the niyyah (intention) is in the heart, and nobody knows of it except Allāh, and verbally stating it is a Bidʿah (heresy)”
Shaykh Ṣāliḥ al-Fawzān حفظه الله تعالى mentioned in the explanation of the Ḥadīth “Indeed actions are by intentions”:
And the niyyah (intention) is in the heart, and nobody knows of it except Allāh, and verbally stating it is a Bidʿah (heresy). So a Muslim does not say “I intend to perform Ṣalāh”, or “I intend to perform Ḥajj”, or “I intend to give Ṣadaqah”, because it is a Bidʿah, and because the place of the niyyah is the heart.
And it is an an action of the heart and not an action of the tongue. And in its outward display is riyāʾ (showing off, an act of minor shirk).
And it is not proven from the Rasūl ﷺ that he verbally stated the niyyah when wanted to perform Ṣalāh, or wanted to perform any action.
Rightly, it has been reported from him ﷺ that in the farewell Ḥajj (Ḥajjah al-Wadāʿ) he entered the state of Iḥrām saying “Here I am for ʿUmrah and Ḥajj” [1]. This is not verbally stating the niyyah.
Rather it is verbally stating as a ritual, and the rite which he intends: Does he inted Ḥajj? Does he intend ʿUmrah? Does he intend to pair Ḥajj and ʿUmrah? Does he intend Ḥajj Ifrād? Does he intend Ḥajj Tamattuʿ?
So it is the rite that he wants to perform, and it does not mean he utters the niyyah. So he should not say “I intend Ḥajj”, or “I intend ʿUmrah”, or “I intend (Ḥajj) Tamattuʿ”, or “I intend (Ḥajj) Qirān”.
And he should not say “I want (to perform) Ḥajj” or “I want (to perform) ʿUmrah”. The statement “I want (urīd)” is not permissible, even if some Fuqahāʾ permitted it. However it is wrong, and whatever has been narrated from the Rasūl ﷺ is concerning specifying the rite that he wants to perform, and not concerning verbally stating the niyyah.
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[1] Ṣaḥīḥ Muslim, Ḥadīth of Anas رضي الله عنه. Ḥadīth number 1251, Kitāb al-Ḥajj, Chapter of Iḥrām and Hadīy of the Nabī ﷺ.
Source: Al-Miḥnah al-Rabbānīyyah fī Sharḥ al-Arbaʿīn al-Nawawīyyah. Pages 23-24.