Mamta (27) has slipped into coma after the attack while her husband Pappu was arrested yesterday following the incident in South-East Delhi's Sangam Vihar area.
The incident took place late Thursday night when Mamta and Pappu were in their room while their three children were sleeping in an adjacent room in their G block residence.
"He then brought a five inch long nail from outside and hammered it on her forehead. After half of the nail went in, he locked the house from outside and fled from the spot," said a police official.
It was the children who saw the mother lying in a pool of blood and untied her.
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They kept crying lying next to her all night.
Pappu who hails from Etah in Uttar Pradesh was arrested yesterday by the police. A case of attempt to murder has been registered against him.