Erdogan personally supervised the controversial construction of Turkey's biggest mosque - designed to accommodate up to 60,000 worshippers and visible to all from its perch on a hill on Istanbul's Asian side.
Its inaugural prayers will be held this night to mark Laylat al-Qadr, one of the holiest nights in the month of Ramadan, when sins are forgiven.
But as the 15,000-square-metre mosque remains unfinished, with several more months of work ahead, worshippers will pray in the courtyard.
A legal bid to axe it was rejected by the courts, but several separate legal processes against it are still pending.
Also Read
But critics have complained that Istanbul has plenty of mosques already and that its design, by female architects Bahar Mizrak and Hayriye Gul Totu, is nothing special.
He also complained that the mosque has been built on a "protected natural site that has given an identity to the Bosphorous for thousands of years".
"It's heartbreaking to see a religious building being erected on top of what God has made more beautifully - nature."
But Ergin Kulunk, an official working on the project, said it would regenerate the whole area.
"In a few years this place will be more beautiful," he said. "The old buildings will renovated, and it will be greener."
Known for his fondness of mega-projects, just a day ago Erdogan inaugurated the fourth-longest suspension bridge in the world across the Izmit gulf. The USD 9 billion Osman Gazi bridge is one of several huge infrastructure projects Erdogan defends as symbols of his government's achievements.