SSridhar writes on BRF:
Jinnah told Islamists like Abu Ala al Mawdudi that he was getting them the land [namely Pakistan] and it was up to them to construct a mosque there. He knew what he was getting into.
Jinnah's letter to the Pir of Manki Sharif promising shariah was produced in the Constituent Assembly in 1949 to push through the Objectives Resolution. It is available in the Constituent Assembly of Pakistan Debates, Volume 5, 1949, Page 46.
While addressing the Karachi Bar Association on 25 January 1948 on the occasion of the Holy Prophet’s birthday, Jinnah said: “Some are misled by propaganda. Islamic principles are as applicable to life as they were 1,300 years ago. The Constitution of Pakistan will be made on the basis of the sharia”.
One of Pakistan’s renowned political scientists, Prof. (Late) Khalid bin Sayeed narrates in his book, ‘Pakistan: The Formative Phase 1957-1948’ Jinnah’s assurances to a group of visiting Islamists thus: “…Constituent Assembly…will be predominantly Muslim…and would be able to enact laws for the Muslims not inconsistence with Shariah Laws and the Muslims will no longer be obliged by un-Islamic laws…”
While portraying himself as a secularist and a Constitutionalist, Jinnah nevertheless asked only an Islamic clergy, Maulana Shabbir Ahmad Usmani who had apostatised Shias, to raise the flag of Pakistan on Aug. 14, 1947. Later, Maulana Shabbir Ahmad Usmani, who had apostatized Ahmedis and calling for them to be stoned to death, was made Sheikh-ul-Islam-i-Pakistan. It was Shabbir Usmani who drafted the Objectives Resolution.
In passionate speeches that Jinnah delivered to masses of the new state of Pakistan, he addressed them as ‘Mussalmans’ instead of as ‘Pakistanis’ and used terms like ‘mujahid’, ‘tenets of the Holy Quran’, and referred to Pakistan as a ‘bulwark of Islam’.
On the other hand, the only time he appeared to be secular was a feeble attempt in his August 14, 1947 speech when he said, "You are free . . ." etc. He neither said nor did anything before or after that to discourage establishing an Islamist Pakistani state.