Mohammed Daheer of Anna Nagar, who ran a grocery shop on Vilar Road, had two sons, Abdul Rahman (22) and Ibrahim. Both the sons, who suspected that Daheer had an extra-marital affair, were staying with their mother Barkath Nisha in Erode. On Thursday, the siblings visited Daheer and Rahman picked up a quarrel with his father over settlement of family properties. Rahman allegedly chided Daheer over his extra-marital affair. Irked by this, Daheer hit Rahman, who was asleep, on the head with a grinding stone in the early hours of Friday and killed him.