The boy, who was critically injured, was found in a room in Kanshi Ram Awas colony of the town, police said.
The minor went missing last evening. Later, his father received a ransom call demanding Rs 5 lakh for his release, they said.
The boy's father informed the police, which put the mobile phones of the callers on surveillance and deployed personnel in some suspected areas of the city.
Fearing action, the abductors left the boy and fled from the spot, with police suspecting that they were locals and knew the trader.
"Kidnappers somehow came to that they have been identified by the police and soon they will be arrested so they tried to kill the boy brutally in anger," the CO added.
The boy has been admitted to Lucknow Medical college, police said.