Wa `alaykum as-salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
2- As for your case, you should fast a day, Thursday or Saturday, with Friday.
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
We are discouraged from fasting on Fridays unless it is Ramadan or the days when fasting is prescribed. So, if you have made a vow to fast forty Fridays, you can fast other days to make up for the number. It is important to remember that Friday is our weekly Eid.
The Prophet (peace and blessings be upon him) said: “If you vow to obey Allah you should fulfill it, but if you vow to disobey then you should not do so.” (At-Tirmidhi)
Allah Almighty knows best.
Editor’s note: This fatwa is from Ask the Scholar’s archive and was originally published at an earlier date.