"If the Bharatiya Janata Party government is formed in Delhi, I promise to bring back the black money and it will be used for welfare schemes for the poor," Modi said.
Addressing a rally in Nawada parliamentary constituency, the Gujarat chief minister said the Congress-led government was not keen to bring back the black money from foreign banks because they have vested interests to save those who deposited the money there.
Modi said India needs a "sevak", not a ruler, to serve the country.
"Give us all 40 seats in Bihar as we want to form a government in Delhi with over 300 seats to take the right decisions."
Asking the people to vote for the BJP, he said the Congress has not fulfilled any promises it had made in the 2009 polls.
"The Congress manifesto is nothing but a dhokha-patra," he said.
On the Nitish Kumar government in the state, he said the administration was "sleeping" when blasts took place at his Patna rally last year.
"The time for promises is gone. Now Bihar needs resolution," Modi said.
In a bid to woo Yadav voters, Modi said he hails from Dwarka and hence it was natural for him to be emotionally attached with the Yadav community.
Taking a jibe at Congress vice president Rahul Gandhi, he said: "The shehzada (prince) of Congress says he has a map of infrastructure in his head. If they took 60 years to draw the map, they will take another 600 years to implement it."