A guest staying at an Upper West Side hotel was arrested after a housekeeper found a gun under one of his pillows and called police, sources said.

Jared Stamm, 22, checked into a room at the Days Inn on West 94th Street in Manhattan on Saturday.

But when the hotel employee entered his room Monday to clean it, he uncovered the black handgun and immediately called cops, sources said. The responding officers found a loaded magazine and a holster, sources said.

Stamm also had several glassine envelopes filled with cocaine, a digital scale and a purple pipe in his room, sources said.

He was charged with possession of a weapon and possession of a controlled substance.