The story related to the holiest city – Indraprastha is mentioned in Padma Purana’s Uttara Khanda.
The sages enquired from Suta about the holiest city situated on the banks of river Yamuna.
Suta narrated the tale which Sage Saubhari had once told Yudhisthira —
Once, Narada and Parvat were travelling through an aerial route, while they were flying over Khandav forest, they were lured by the beautiful sight of river Yamuna. They decided to take rest for a while. Both of them descended down and entered river Yamuna to take their bath. Meanwhile, King Shibi who ruled over Ushinar saw them. He eagerly waited at the bank of Yamuna. When Narada and Parvat emerged out of the Yamuna, they found king Shibi eagerly waiting for them. Meanwhile king Shibi had noticed the remains of numerous ‘havan-kundas’ (oblation-altars) spread in a large area.
After the formal exchanges of pleasantries were over, King Shibi asked Narada about those havan- kundas.
Narada replied–During ancient times Indra had performed numerous Yagyas at this place to express his gratitude to Lord Vishnu, with whose blessings he had regained the heaven from the clutches of Hiranyakashipu.
In course of time, this place became famous as Indraprastha. This sacrosanct place is holier than all the holy places combined together. Indraprastha is spread in the area of one yojana from east to west and four yojanas from north to south.