A male pensioner in his seventies was seriously injured when he was stabbed near his home in Clondalkin in west Dublin on Monday evening.
Neighbours called gardaí after the man was found in the roadway with stab wounds
The man was taken to Tallaght hospital where his condition is described as serious.
A woman in her seventies was arrested at the scene and is being questioned at Ballyfermot Garda station.
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She can be questioned for 24 hours before being charged or released.
Gardaí believe the injured man and the arrested woman are a couple and are treating the stabbing as a domestic incident.