1 John 3:20
Whenever our hearts condemn us. For God is greater than our hearts, and he knows everything.

God, who knows everything, hears the prayers of everyone (disciple or an unbeliever). If he didn't, he would not be all knowing

The question is really whether or not God will answer a person's prayers while he is continues to be in sin. For the most part, the answer is no.

1 John 5:14
This is the confidence we have in approaching God: that if we ask anything according to his will, he hears us.

Sin is rebellion against God, and while we are in sin we are not doing the will of God. So if God is to answer our prayers, our prayers must be according to his will not ours, and when we are sinning we are carrying out our will not God's will. So, even though God will hear all of our prayers, while we are in sin we are not in his will and our prayers will not be answered -- at least not if they are focused on asking God to help you in sinning.

On the other hand, God certainly hears and answers the prayers of the sinner who seeks to repent from sin and who asks God to cleanse him yet again of his sin. God is, after all, loving and forgiving.

Ephesians 4:30
and do not grieve the Holy Spirit of God, with whom you were sealed for the day of redemption.

What does it say? It says do not grieve the Holy Spirit of God. I understand and learn two things from this verse.

1) God (Holy Spirit) lives in me. It’s not a small portion of God given to us at the time of baptism but God himself comes to live within us. This truth has changed the way I pray.

The God who created the universe and everything around us, lives in me; fully.

2) The Holy Spirit can be grieved but it doesn’t leave me. It has been given to me for the day of redemption.

When I sin against God; He is grieved within me but He doesn’t stop listening to me or leave me. The Holy Spirit convicts us of our sins so that we can be led to repentance.

But repentance is not possible without talking to a brother or a sister and to God simultaneously.

When I sin against people; the tendency is to stop talking. Similarly when I sin against God; the tendency is to stop praying. In fact it should be the other way round. When I have sinned against someone; I need to talk with an intention to reconcile, to apologize and to resolve.

Has it happened with you that you sinned and stopped praying till you confessed?

Let’s remember that God is all-knowing; he will listen to your prayer even when you are in sin but not answer it according to your will. This in no way means that we can continue sinning and continue to pray at the same time.

Galatians 6:7
Do not be deceived: God cannot be mocked. A man reaps what he sows.

Pray with in intention to repent from your sins. Ask God to give you strength to confess, to reconcile with your brother/sister.

Challenge

Make a banner for God expressing your commitment that I will never stop praying to Him; no matter what happens. Hang it somewhere in your room where it is visible to you.