Gregory Todd shows the engagement ring outside Hull crown court. Photograph: Dave Higgens/PA

A man who forgave his partner for nearly killing him when she plunged a kitchen knife into his back brought an engagement ring to court in the hope a judge would let her walk free.

But when Tiffany Baillie was sent to prison for three years at Hull crown court, Gregory Todd said he understood why Judge Michael Mettyear had no choice but to jail her.

Todd, a 48-year-old chef, wrote to Mettyear pleading with him to not to send Baillie to prison so he could give her the ring. He said he had forgiven Baillie, 32, for stabbing him with a "substantial" knife, seriously injuring him.

Todd was sat in the public gallery as Mettyear jail Baillie after explaining how most crimes of this type attract much longer sentences.

Outside court, Todd praised the judge for his leniency.

He said he had not been allowed to go down into the cells to show his partner the ring but that his barrister had taken it and it fitted.

Mettyear told Baillie how the offence would normally attract a prison sentence starting in the nine to 16-year range afterhearing she had plunged the knife into Todd's back while he slept at their flat in Hessle, Hull, on 4 December last year when the pair returned to the flat after a night out drinking.

Mettyear said: "You armed yourself with a substantial kitchen knife and stabbed him with it in the back. It was a forceful blow with substantial penetration of his body."

Todd suffered injuries to his colon, a kidney and his pancreas. The judge said: "What you did could have killed him or caused long-term serious injury."

Baillie, who is also a chef and has a 12-year-old son, admitted causing grievous bodily harm with intent at a previous hearing. The judge said he was giving Baillie more credit than normal for the mitigation provided by Todd's forgiveness.

He said: "Your victim has completely forgiven you. He has visited you in prison and has written to me stating in detail his view of you and what should happen to you."

Mettyear read part of Todd's letter to the court: "She made a huge mistake she will regret for the rest of her life. Please allow me to present her with the ring and leave this courtroom today to continue with our lives. I promise I will not let you down."

Outside court, Todd said: "I think he (the judge) was very fair. I'm not completely happy with the result but I think he was as lenient as he could be."

Asked what he said to the judge in his letter, he said: "That myself and Tiffany could walk out of the court and get married and that we wouldn't let him down and she could be with her son and we could get on with our lives."

Todd showed reporters the white gold and diamond engagement ring and said he was hoping Baillie would be out in little more than a year. "I just want to be with Tiffany. That's all I can say."

He added that he was fully recovered after spending three months in hospital. Emergency surgery saved his life.