The incident took place at Pul Prahlad area last night and the victim has been identified as Neeraj.
Neeraj was stabbed allegedly by brothers Pradeep and Sanjay following argument over not giving a cigarette, ACP (South-East) Ajay Chaudhury said.
Neeraj along with his friends Rajesh Shahrukh and Paua were sitting when Pradeep came there.
"Pradeep asked Rajesh to give him cigarette which he refused. On this Pradeep started quarrelling with him. Neeraj intervened in his support and they had a scuffle with Pradeep, who picked up a knife from the near eatery.
"Pradeep's younger brother Sanjay also joined the fight. Sanjay caught Neeraj from behind and Pradeep stabbed Neeraj on the left side of chest. Neeraj was rushed to AIIMS Trauma where he was declared brought dead," Chaudhury said.
Pradeep was arrested in the wee hours today, while Sanjay is absconding.