Rapper Nas is asking a judge to set a firm custody schedule with his ex-wife Kelis so he can spend time with their son on a regular basis.

The One Mic star, full name Nasir Jones, claims the singer is currently only allowing him visitation with eight-year-old Knight "when she deems it convenient for her", even though he has done his best to co-operate with Kelis following their separation in April, 2009, when she was seven months pregnant with their kid.

According to court papers obtained by TheBlast.com, Kelis has been choosing when Nas can see his boy, but will then "refuse to set up time" for the father and son to bond for months.

He wants an official custody schedule put in place, and has suggested Knight spends the first, third, and fifth weekend of every month with his dad. Nas has also proposed having Knight stay with each parent for their own birthdays, while celebrating Mother's Day with Kelis and Father's Day with the hip-hop hitmaker.

Other notable dates have also been split up, with Nas suggesting Kelis spends holidays like Independence Day, Halloween, and Thanksgiving, as well as Knight's birthday, with their child in even years, while the rapper should have custody during odd years.

Nas and Kelis wed in 2005, and finalised their divorce in 2010.

The rapper is also dad to 23-year-old daughter Destiny, from his relationship with ex-girlfriend Carmen Bryan, while Kelis welcomed another son in 2015. She has never publicly revealed the identity of the boy's father.