Sonia Gandhi is credited with driving the social agenda of the government.
The dinner was held two days before votes polled in the Lok Sabha election are counted May 16. The prime minister will submit his resignation to President Pranab Mukherjee May 17.
Manmohan Singh, who became India's 14th prime minister and the first technocrat to rule the country, will continue to be a member of the Rajya Sabha after he demits office.
The 81-year old prime minister had Jan 3 addressed his final press conference and announced his retirement after a decade at the helm of two successive UPA governments.
