Answered by Shaykh Yūsuf Badāt

Question:

Is a vow (nadhr) obligatory to fulfill where the vow has been made without moving the lips? In this case, the tongue was moving.

Answer:

بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم

In the name of Allāh, Most Gracious, Most Merciful.

Jazāk Allāh Khayr/ Thank you for contacting Mathābah.

Islamicaly, a vow comes into effect when there is tongue movement. Lip movement is not required. The voice does not need to be heard, while articulating the vow. – (See: Al-Fatāwā Al-Bazāzīyah, Vol 1, Page 95, Dār Al-Kutub Al-‘Ilmīyyah)[1]

Only Allāh knows best

[1] والنذر لا يكون الا باللسان ولو نذر بقلبه لا يلزم خلاف النية لان النذر عمل اللسان والنية عمل القلب – البزازية ج١/ ص٩٥ دار الكتب العلمية