Mohammad Rafiq, a 65-year-old retired Pakistani Air Force officer, was the first of the three people who approached the Norwegian mosque attacker, the administration claimed on Saturday.
Police in the area have said that Sunday's attack al-Noor Islamic Centre is being investigated as a "possible act of terrorism".
The suspected shooter at the al-Noor Islamic Centre near the Norwegian capital - a young, white male carrying several guns - had expressed far-right, anti-immigrant views online, assistant chief of police Rune Skjold told a news conference.
The suspect had been apprehended after the attack, in which shots were fired but no one was hit, with Rafiq having overpowered him inside the mosque before police arrived.
Only three people were present in the mosque at the time of the attack, preparing for the next day's celebration of Eidul Azha festival, mosque spokesman Waheed Ahmed told Reuters.
“These people showed great courage,” Skjold added.
“I suddenly heard shooting from outside,” Rafiq told Reuters via an interpreter, adding that a man then entered the building with guns and pistols.
“He started to fire towards the two other men,” Rafiq said, adding that he had then grabbed the attacker, holding him down and wrestling the weapons off the attacker.
His eye red and one hand swollen, Rafiq, who has lived in Norway for the past two and a half years, said he was still recovering from the attack.
“He put his finger inside my eye, up to here; full finger inside my eye,” Rafiq added.
The attacker, who has not been named, was also suspected of killing one of his own family members, a young woman who was found dead at his home, police said earlier.
The mosque had implemented extra security measures this year after the massacre of more than 50 people at two New Zealand mosques by a suspected right-wing extremist.
Norwegian Prime Minister Erna Solberg said police had ramped up security on Sunday as thousands of Muslims gathered at mosques for the Eid celebration.
While the government continuously tries to combat hate speech, more must still be done, she added.
“We are trying to combat this, but it’s a challenge. I think it’s a word-wide challenge in a sense,” Solberg said.
In 2011, anti-Muslim neo-Nazi Anders Behring Breivik massacred 77 people in Norway’s worst peacetime atrocity, the majority of them teenagers at a youth camp.