Pakistan: A secular Muslim state

While the refusal of the provinces of the Indus Valley region to stay as a union with the rest of the subcontinent to ensure protection of the Muslims and their religious rights, nothing more was required to ensure this.
This means that mixing religion with state affairs is not what Jinnah and the constitution of Pakistan stood for.
Articles 20, 21 and 22 of the Pakistani constitution clearly state:

-every citizen has the right to believe, practice and propagate their religion

-every religious denomination/sect has the right to establish, maintain and manage its religious institutions

-no person can be compelled to pay any special tax to be spent on the propagation or maintenance of a particular religion or religious institution other than his/her own

-no person attending any educational institution can be required to attend religious ceremonies, worship or receive education of a religion other than his/her own.

-no discrimination against any community in grant of tax exemption or concessions for religious institutions

-no discrimination in admission to educational institutions receiving public funds on grounds of race, religion, caste or place of birth
(Exceptions: quota system is permissible for advancement of any socially or educationally backward class of citizens).

So clearly this original constitution is proof of Pakistan's secularism. The later Sharia laws imposed by Zia Ul-Haq were irrelevant as he was not a founding member of the Pakistani constitution.

A famous quote by the founder of modern Pakistan Muhammad Ali Jinnah:
"You are free; you are free to go to your temples. You are free to go to your mosques or to any other places of worship in this State of Pakistan. You may belong to any religion, caste or creed --that has nothing to do with the business of the State."

It is clear from the quotes of the founding father and the constitution that Pakistan owes it's loyalty to anyone other than it's citizens and does not belong to any Pan-Islamist ideologies.

There are Pan-Islamists out there who try to propagate Islam over national identity.
Another quote of his comes as a challenge to these Islamists who have tried to break Pakistan's secularism and impose Pan-Islamism (A 'religious duty' from how they see):

"We are now all Pakistanis--not Balochis, Pathans, Sindhis, Bengalis, Punjabis and so on--and as Pakistanis we must feet behave and act, and we should be proud to be known as Pakistanis and nothing else."