An Ottawa man has been found not guilty of sexually assaulting his wife because he believed he had the right to have sex with her whenever he liked.

The prosecution failed to establish the man knew his behaviour was criminal, said Ontario Superior Court Justice Robert Smith.

"I find that the accused probably had sex with his wife on many occasions without her specific consent, as both he and she believed that he had the right to do so," the judge added.

The court heard that the man was part of an arranged marriage in Gaza. His wife is a Palestinian who grew up in Kuwait. The couple settled in Ottawa after marriage.

The woman told the jury that although she did not always consent she also believed her husband had the right to sex, reported the Ottawa Citizen.

The couple separated in 2013 and after speaking to a police officer about a dispute over child arrangements, the woman came to understand she had the right to refuse sex with her husband.

She then complained to the police that in 2002, her husband grabbed her wrists, pulled her to the sofa and had sex with her even though she asked him to stop three times.

This charge was brought to court, which the man denied. He said that at the time he had just undergone a hair transplant and his doctor had told him to abstain from sex for two weeks after the procedure.

He said at the time of the incident he was following his doctor's advice, and so the incident could not have happened.

But the judge said: "The accused did not call any medical evidence to show this was standard medical practice, and I find his evidence in this regard does not accord with common sense to a reasonably informed person."

The court added the man was argumentative and evasive as a witness, and he rejected his account as not believable.

But the judge still said he could not find the accused guilty of a crime.

Judge Smith said: "Marriage is not a shield for sexual assault. However, the issue in this trial is whether, considering the whole of the evidence, the Crown has proven the allegations beyond a reasonable doubt."

Carrolyn Johnston of the Ottawa Coalition to End Violence Against Women said the ruling highlighted persistent myths about sexual assault.

She said: "Any sexual contact without explicit and ongoing consent is sexual assault — regardless of the relationship."

The women's group pointed out that under Canadian law sexual assault legislation was amended to include sexual assault against a spouse in 1983.