Answered by: Aalimah Nasima Umm Hamza
Assalamu Alaikum Wa Rahmatullah
My question is regarding mental oaths. If I have made a mental oath but have not done it properly i.e I did not specify what oath I was making but only used the words, ‘qasam wallah’ … or ‘walaqtubillah’ in my mind, in this case, does it make the oath valid?
Mufti Menk said that mental oaths are not valid or binding and Mufti Siraj Desai pointed out that mental oaths have to be uttered verbally, but I would really like your opinion as well.
بسم الله الرحمن الرحيم
In the name of Allah, the Most Gracious, the Most Merciful.
Oaths made in the mind are not valid oaths. An oath must be made verbally, with the movement of the mouth and tongue as a minimum.
“ إِنَّ اللَّهَ تَجَاوَزَ لأُمَّتِي مَا حَدَّثَتْ بِهِ أَنْفُسَهَا مَا لَمْ يَتَكَلَّمُوا أَوْ يَعْمَلُوا بِهِ ”
The Messenger of Allah (ﷺ) said:
“Verily Allah forgave my people the evil promptings which arise within their hearts as long as they did not speak about them or did not act upon them.” 
Only Allah Knows Best
Answered by Aalimah Nasima Umm Hamza
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Sahih Muslim, Hadith Number 127
This answer was collected from DarulIftaBirmingham.co.uk, which is run under the supervision of Mufti Mohammed Tosir Miah from the United Kingdom.