"We will walk with you side by side every step of the way...when are we going to wrap up this sit-in will be decided by us [opposition] and not anyone else," he declared after meeting the leaders of opposition parties.
He said the sit-in will continue till their demands are met.
"Today, the opposition parties have decided that we ourselves will plan the future strategy for the Azadi March, not you," said the JUI-F leader in an open message to the ruling PTI.
"We want to pull Pakistan out of isolation," said the JUI-F leader, adding that there is something going on at every front for the country to struggle with.
"Imran Khan was first selected, now he is rejected and I would rather say that things have gone beyond 'selected' now," said Fazl to the crowd, reiterating the demand for the Prime Minister to call it a day.
"We are nearing the objective of Azadi March. We're frustrated because of "illegitimate" rulers, but are showing restraint and our frustration will be over the moment they [rulers] go home and fresh elections are announced," he added.
Rehman severely criticized the PTI government's economic policies, saying the country's economy is now "fully in the hands of the IMF." "We cannot tolerate further decline of Pakistan," he added.
On the fourth day of Azadi March, the JUI-F chief told participants of the 'Azadi March' to remain steadfast as the day is not far when the government will be sent packing.
About the government's suggestion to file a complaint with Election Commission of Pakistan (ECP) if the elections are rigged, Fazl said that the Commission is "even more helpless than us."
Fazl said if the Election Commission was not so helpless, such a large crowd wouldn't have assembled in Islamabad.
"We have decided not to go to any court or Election Commission," he said. "Only a parliamentary committee will decide about rigging."
Fazl said a case of the PTI's foreign funding has been heard by the Election Commission for the past five years but no verdict had been given on it.
He asked: "If it couldn't decide about the foreign funding case then what decision the ECP can give on other matters?"
Fazl said that D-Chowk was quite a small place for such a gathering.
"H-9 is an open space-D-Chowk is quite small for a gathering like this...whatever decision we take, we will do so in consensus with all opposition parties," he said.
Fazl said that at present the entire city has been closed down but he can shut down the country as well.
"We will shut down the entire country as well and continue our battle," he said.
Fazl lashed out at Prime Minister Imran. "Do you expect this novice will teach us politics? Now people born with a golden spoon in their mouths will teach us politics and that too, the politics of the poor?" he asked.
Fazl issued a stern warning to Prime Minister Imran, warning him that his Azadi March would throw him away.
He said: "Imran Khan, listen to me. This movement and flood of people will force you out of the prime minister's seat."
Criticizing the Prime Minister, Fazl said that it was unfortunate that he was occupying such a coveted seat.
"We know about you and your character very well," he said, adding: "We are also aware of ourselves and our characters."
According to Maulana Abdul Wasay of the Muttahida Majlis-i-Amal, all JUI-F members of National Assembly have submitted their resignations to party chief Fazlur Rehman.
Sources told Business Recorder that the resignations will be used, if required, according to the party's strategy.
National Assembly Speaker Asad Qaiser has called upon the leadership of political parties to agree to hold a "national dialogue" at the platform of the Parliament to resolve the ongoing deadlock.
In a series of tweets, Qaiser said it is important for the political leadership to be on the same page to counter internal and external challenges and economic issues faced by the country "for which a national dialogue is the need of the hour".
"Parliament is the sole representative institution of the people and as the representative of people's wishes it is ready to play every role possible," the speaker wrote.
Noting that the superior judiciary and leaders of opposition parties too have previously suggested resolving national issues through a parliamentary-level dialogue, Qaiser urged the country's political leadership to "cooperate" and present recommendations in this regard.
Prime minister's aide Dr Firdous Ashiq Awan advised JUI-F chief to "wait for four years", when the country's next general elections will be held.
In a series of tweets, Awan said: "Maulana sahib, it is up to Pakistan's public to decide [who] comes to power and who leaves. Wait for four years. Listen to your own speeches [delivered] in past assemblies for guidance."
In another tweet, the premier's adviser remarked: "On one hand, a parliamentary meeting is being chaired by Prime Minister Imran Khan for Pakistan's development, strengthening of democracy and the prosperity of the people. While on the other hand, plans are being hatched to [instigate] anarchy, mayhem and block the way of the public prosperity.
"The entire nation is watching what agenda and priorities [each side] have."
The protest in federal capital is the first concerted opposition's challenge Prime Minister Imran Khan has faced since he won a general election in 2018.
Security remained tight in Islamabad.