Who suggested digging of trench during the Battle of Trench?

a) Hazrat Abu Bakr (R.A)

b) Hazrat Usman (R.A)

c) Hazrat Khalid bin Waleed (R.A)

d) Hazrat Sulman Farsi (R.A)

Hazrat Sulman Farsi (R.A) suggested digging of trench during the Battle of Trench. It took six days to dig it. This battle was fought between Arab and Jewish tribes in 627 AD (5 AH). It lasted for about 30 days.