Does Allah Accept the Du`a of Sinners?
Question

The Prophet (peace and blessings of Allah be upon him) said that the one who eats or wears haram things will receive no answer (to his Du`a). Is the Du`a of the sinner not answered?.
Praise be to Allah.Does Allah Respond to Sinners’ Du`as?
Answer to the Du`a of one who calls upon Allah is, in principle, an indication of the righteousness and piety of that person, but it does not always indicate that. A sinner’s Du`a may be answered as a means of leading him gradually towards his punishment, or for another reason. Allah answered the prayer of the devil when He said (interpretation of the meaning):
{‘O my Lord! Give me then respite till the Day they (the dead) will be resurrected.’ Allah said: ‘Then verily, you are of those reprieved’.} [Al-Hijr 15:36-37]
This response was not an honour for him, rather it was a humiliation, to increase his sin so that his punishment would be greater – we seek refuge with Allah.
The Du`a of Oppressed Sinners: Is It Accepted?
And it is proven that the Prophet (peace and blessings of Allah be upon him) said: “The prayer of the one who is oppressed is answered even if he is an evildoer, and his evildoing is upon himself.” (Narrated by Ahmad; Sahih Al-Jami`, 3382)
Answered Du`as: Not Always a Sign of Righteousness
Similarly, the fact that a Du`a is not answered does not always mean that the one who is praying is corrupt. There are some prayers which Allah did not grant our Prophet Muhammad (peace and blessings of Allah be upon him). He (peace and blessings of Allah be upon him) said: “I asked my Lord for three things, of which He granted me two…” (Narrated by Muslim, 2890)
The Wisdom Behind Unanswered Duas for the Prophet
Allah did not answer some of the prayers of His Prophet (peace and blessings of Allah be upon him) for an important reason, which was to teach mankind that he had no control over anything, rather everything was under the control of Allah. (Sharh Al-Arba`in An-Nawawiyyah, and Kitab Ad-Du`a by Shaykh Muhammad Al-Hamad)
For more details, please see the following answers:
Conditions of Accepting Du`a
Sin and its Effects on the One Who Commits it
How to Make Du’a
Why Doesn’t Allah Answer Your Du`a?
Du`a is worship
How to Make Du`a During Prayer
And Allah knows best.