A mom was stabbed and left to die inside a Harlem building by her ex-boyfriend — who waited for hours to ambush her and unleashed his attack even as she begged him to stop, sources and workers said.

The unidentified 47-year-old mother of four cried out her attacker’s name as he stabbed her multiple times, then left her lying in the blood-spattered hallway of a six-story rental building on West 129th Street early Monday, according to law enforcement sources and building employees.

A porter called 911 upon spotting the woman drenched in blood and clinging to life near the elevator on the third floor of the building around 4:25 a.m., cops and sources said.

Lyron Middleton said he found the building resident — who has a teenage autistic son — as he cleaned the staircase.

“I saw the blood a

See Full Page