'I tried pushing him off her': Daughter relives mother's fatal stabbing attack

A Sydney woman, who saw her father stab her mother to death, begged and frantically tried to stop him while screaming for help, she has told a court.

Ola Haydar, who was 18 at the time, told the NSW Supreme Court she heard a scream at her Bexley home and ran into the kitchen to see her father, Haydar Haydar, stab her mother, Salwa Haydar, in the back in early 2015.

Ms Haydar said she "tried to get in the middle of it" but her father kept going.

"I was trying to hold his hand back, the one that held the knife," she said on Wednesday.

"I tried pushing him off her but I couldn't."

Ola Haydar told a court that she screamed for help when her father attacked her mother. Picture: Facebook

Breaking into tears, Ms Haydar said she was "begging him to stop" and "screaming and screaming for help".

She cried out, "what are you doing? Oh my God you're going to kill her" but her father responded, "no, it's fine" and "why are you screaming? Stop screaming."

Haydar, 60, is on trial and has pleaded not guilty to murder, wounding with intent to cause grievous bodily harm and reckless wounding, but has pleaded guilty to manslaughter.

The Crown says the former taxi driver suspected his wife of having an affair and stabbed her 30 times.

On Wednesday Ms Haydar told the court that two of her fingers were cut when she tried to save her mother, but she wasn't paying attention to herself at the time.

Salwa Haydar was killed back in 2015. Picture: AAP

She said she heard her father call her mother the Arabic word for "slut" during the attack and heard her mother say: "I didn't do anything".

Ms Haydar said she went to the phone to get help and her father turned around.

"He looked at me and said, 'what are you doing?' And he continued," she said.

"He'd look back and continue."

Mr Haydar cried and held his head in his hands in the dock.

Ola Haydar was just 18 years old when her mother was mother was killed. Picture: AAP

Crown prosecutor Michael Barr said in his opening statement that Mr Haydar and his wife, a drug and alcohol counsellor, had talked often about separating.

Mr Barr said Haydar suspected his wife of being unfaithful after he found messages to a co-worker on her phone.

Haydar's defence case would be that he was impaired by an abnormality of mind at the time, the prosecutor told the court.

Haydar's uncle had suddenly died and his mother, who had dementia, had hardly recognised him when he visited her in Lebanon.

The trial is before Justice Peter Garling alone.

- With AAP.