Many believed he resigned because of the 'fear of Buhari.His resignation has since been approved by President Buhari.
In his own words, Read why he resigned.

"Tomorrow, I will be six years as Comptroller-General of Customs and after wide consultations, I decided to personally meet him and express my gratitude and appreciation for serving for six years.
"And the only way the Nigeria Customs Service can move forward, I feel personally is my making a sacrifice."The sacrifice is to give chance to others so that they can come up and continue with the legacies and the reforms and structure that I have put in place.’’

http://skyblings-entertainment..com/2015/08/resons-behind-customs-comptroller.html#sthash.5WnJe9Jt.dpuf

tell that to the marines

Really?

This man obviously listened to his good advisers. By this singular act of voluntarily resigning, he has denied President Buhari of the usual orgasm he enjoys by sacking, and has thus, given baba a premature eja-cu-la-tion. I am speaking politically though, and not biologically.

this the first time am hearing a GOVT. Official resigns voluntarily.... i guess some other should follow his example,Esp when you know you have over stayed your welcome in a public office