Hadhrat Ibrahim bin Adam (May Allah Ta’ala shower His Mercy on him) said that no one achieved any high station with only Salaat, Fasts, Haj, Zakaat and Jihad.  Only that person achieved greatness and only that person was blessed with Ma'arifah , who earned his living through Halal sources and realized (i.e. is mindful) of what he eats.  This is because with even a mouthful of Haraam, neither the Dua is accepted nor any desire and yearning of worship is developed.  Understand it well that the base for every good act is Halal living. 
Hadith:  The Holy Prophet (Sallallahu alaihi wa sallam) says: The person who avoids eating Haram food, Allah Ta’ala decides about him that I (i.e. Allah Ta’ala) will feel shy of taking him to account.

And also said: The person who gets tired searching for Halal earnings and comes to his house fully tired, when he sleeps, all his sins are forgiven and when he gets up in the morning, Allah Ta’ala is happy with him.

And said: Until a Muslim does not leave what is not doubtful for the fear of what is doubtful, he will not reach the status of Atqiya (Those who fear Allah Ta’ala)

Hadhrat Abdullah bin Umar (May Allah Ta’ala be well pleased with him) says: Praying after eating Haraam food is like building a house without any foundation, which will not be strong and lasting.

Hadhrat Pirane Pir Shaykh Abdul Qadir Jilani (May Allah Ta’ala shower His Mercy on him) says: Haraam food busies a person in this world (Dunya ) and creates love for sins.  Halal food creates interest in the works of the hereafter i.e. Aakhirah and makes one love the obedience of Allah (Subhanahu Wa Ta’ala), which earns one the Qurb (closeness) of Allah Ta’ala.

Hadhrat Abdullah bin Abbas (May Allah Ta’ala be well pleased with them) says: If a worshipper ( A'abid ) worships so much that his back bends like an arch and fasts so much that he becomes thin like an arrow, by Allah Ta’ala, this deed of him