"Around 26 lakh toilets were constructed in Bihar, Uttar Pradesh, Odisha and Jammu and Kashmir in the past week, which was observed as Swachhagraha week", the prime minister said.
But the PM will not disturb his daily official routine; he will continue meeting people and officials and clearing files as scheduled, sources said.
MIM party chief Asaduddin Owaisi hit out saying, "If the prime minister wants to fast for losing whole session of parliament, I want to ask the honourable prime minister where is his sense of duty lost, wherein, in the past four years thousands of farmers committed suicides".
Amit Shah will observe a hunger strike in Hubli in poll-bound Karnataka, while party MPs will fast in their constituencies.
Last week, the entire second leg of the budget session was a complete washout without discussion due to protests by the opposition parties on various issues.
Modi's decision, which may be the first time a Prime Minister is observing a fast, will be part of the Bharatiya Janata Party's day-long hunger strike that day to protest against the disruption of Parliament by the opposition. "I will be fasting".
Option open for Siddaramaiah to contest from Badami too
The 224-member Assembly expires on May 28 in the state where the Congress is now in power, with 122 seats against the BJP's 43. A "fake" list of Congress candidates for the upcoming assembly elections in Karnataka is being circulated on social media.
Earlier, Modi was received by Bihar Governor Satyapal Malik, Nitish Kumar, Union Minister Ram Vilas Paswan and several other BJP leaders.
Congress president Rahul Gandhi had on Monday (April 9) led his party in a nationwide daylong fast against caste violence, communalism and the non-functioning of Parliament, for which the UPA blames the ruling BJP.
Prime Minister slammed the Opposition allegedly for trying to break up society and "putting hurdles, from the Parliament to the streets" in the Governments' efforts to uplift the poor. While Interacting with media in New Delhi Surjewala said, "This is a farce of a fast by the Modi government".
In a statement, the BJP said that Prime Minister Modi along with all the party MPs will observe fast on Thursday, to reveal the "undemocratic and anti-development face of the Congress party, which stalled the proceedings of Parliament during the Budget Session".
Only two out of eight bills planned for this session could be introduced.