A 25-year-old man was killed with a spade as he slept at the home of a couple with whom he stayed in Rajasthan's Hanumangarh district, police said on Tuesday.
He was allegedly killed by Sitaram (42), they said.
Police described the victim, Rakesh, as the woman's lover, staying at the home with the consent of the couple.
The incident occurred in the early hours of Tuesday in ward number 1, Station House Officer (SHO), Sangariya, Inder Kumar said.
"Rakesh had a love affair with Sitaram's wife, aged 35, for sometime. He was living with the couple in their house. The couple have three children," the SHO said.
"A heated argument broke out between Sitaram and Rakesh last night. Rakesh went to sleep and later Sitaram attacked him, leaving him dead on the spot," Kumar said.
Sitaram, his wife and two others have been rounded up and are being interrogated, he added.