What was the battle in which Khalid bin Waleed besieged a city with a trench around it and filled up the trench with camels to cross it?

i remember reading about a battle in which the muslim army under Khalid bin Waleed laid siege to a city with a trench around it and Khalid RA had the old and weak camels slaughtered to fill up the trench and cross it. What was the name?