A “generous” elderly man was brutally stabbed to death inside his Manhattan apartment early Monday by a roommate he’d taken in just days earlier, after his mother had kicked him out, cops and neighbors said.

Alon Riabichev, 45, is facing murder charges in the vicious slaying of Lev Vayner, 80, after an argument turned deadly at their 37 Overlook Terrace residence in Hudson Heights around 3:15 a.m., police and sources said.

Vayner, who neighbors described as selfless, was stabbed in the abdomen and neck before he died in his first floor unit, police confirmed.

“It’s terrible. Terrible. He was very generous and he tried to help,” Juanita Abreu, who lived on the block, said of Vayner.

“I don’t have any explanation. I can only tell you that this neighborhood was good for a very long time.

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