Wajah means the reason or cause (for something). Bewajah is the opposite – without any reason or cause. It is of Persian origin.
Here are the lyrics and translation of the absolutely wonderful song by Nabeel Shaukat Ali from Coke Studio Pakistan. Simply enthralling! Enjoy.
Hijr-e-yaaraa naa sataa bewajah
Hijr-e-yaaraa naa sataa bewajah
Ban gaya tu kyun wajah bewajah
Ban gaya tu kyun wajah bewajah
Dil se keh waqt ruk jaa paagal
Chal pada karne ye wafaa bewajah
Hijr-e-yaaraa naa sataa bewajah
Ban gaya tu kyun wajah bewajah
Oh pain of separation (from the beloved), don’t torment me, for no reason
Oh pain of separation (from the beloved), don’t torment me, for no reason
Why have you become a reason, for no reason?
Why have you become a reason, for no reason?
Oh time, do tell my heart to be wise and stop this madness
It is determined to be faithful and in love, for no reason
Oh pain of separation (from the beloved), don’t torment me, for no reason
Why have you become a reason, for no reason?
Main use bhool chuka, bhool chuka
Main use bhool chuka, bhool chuka
Main use bhool chuka, bhool chuka
Baat ae dil na badha bewajah
Baat ae dil na badha bewajah
Hijr-e-yaaraa naa sataa bewajah
I have already forgotten her, forgotten her
I have already forgotten her, forgotten her
I have already forgotten her, forgotten her
Oh heart, don’t complicate the matter, for no reason
Oh heart, don’t complicate the matter, for no reason
Oh pain of separation (from the beloved), don’t torment me, for no reason
Naam lene ka iraada bhi na tha
Naam lene ka iraada bhi na tha
Naam lene ka iraada bhi na tha
Chal pada zikr tera bewajah
Chal pada zikr tera bewajah
I had not meant to even mention your name
I had not meant to even mention your name
I had not meant to even mention your name
Your mention came up somehow, for no reason
Your mention came up somehow, for no reason
Unse milne ki wajah koi nahin
Unse milne ki wajah koi nahin
Unse milne ki wajah koi nahin
Dhoondhta kyun hai wajah bewajah
Dhoondhta kyun hai wajah bewajah
Hijr-e-yaaraa naa sataa bewajah
Ban gaya tu kyun wajah bewajah
There is no reason, to meet with her
There is no reason, to meet with her
There is no reason to meet with her
Why do you search for reasons, for no reason?
Why do you search for reasons, for no reason?
Oh pain of separation (from the beloved), don’t torment me, for no reason
Why have you become a reason, for no reason?
With inputs from http://www.zenithlyrics.com/2015/08/bewajah-nabeel-shaukat-ali-coke.html
urduwallahs 
This is one of my most favorite songs ever!