Farid Ahmed was in a side room of Al Noor Mosque when a gunman opened fire in March 2019.
His wife Husna was in the main chambers.
He recounted the story piece by piece to about 50 pupils of St Kevins College yesterday, starting at the car ride to the mosque, to finding out his wife was dead and ending with the conversations he had with his 15-year-old daughter later that evening.
The main thing he wanted the pupils to take away from the meeting?
"They should be compassionate."
Every person on Earth shared a familial bond as humans, regardless of religion or race, he said.
He could have held on to the hate and depression after his wife was killed, but felt it was more important to let it go and live with a clean heart.
He and his daughter still cried over the loss of Husna, but it was not out of anger or despair, but out of "natural love" for her.
It is not the first time he has forgiven somebody who had changed his life forever.
Mr Ahmed has used a wheelchair for more than 20 years after he was hit by a drunk driver.
"Physically, it was very tough, but in my heart I felt very happy."
He was alive and that was something to thank God for, he said.
"Life is not a bed of roses.
"If you focus on the negatives, life will be tough.
"It will have ups and it will have downs.
"All you are to do is try maintain your balance."
He had faith the younger generation would take his message to heart, as he had already seen the compassion they were capable of.
After the mosque attack, he was sent letters and cards from primary school pupils all over New Zealand and he had seen fundraisers held by them.
Just as New Zealanders wanted to be the best in the world at rugby or cricket, he challenged the pupils to try make it the No 1 country in the world in compassion.
