When you are surrounded by Arabic people and in order to ensure you are saying the truth they tell you to "say wallah"
Mark: "That hot girl Trixie was all over me last night"
Ahmed: "Really? Say wallah"
Mark: "Wallah man, I swear"
by Leanasaur January 3, 2010
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"Wallah" is the Arabic way of saying "On God" as in "I swear".

"Say Wallah" can be used to actually question whether one's being honest or not, but that's not often the case, Most of the time it's just the Arabic way of saying "No shit?"
person1. bro, i just found out Axel's mother has cancer?
person2. Shiit. Say wallah?
person1. On god, man.

person1. EY bro i just realized its friday
person2. mhm, so?
person1. we don't got school tmr!!
person2. Say wallah? such a smart discovery you just made.
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