What are the consequences of uttering words of disbelief (kufr)
Question

We are a group of young men, and yesterday we were playing chess. When he made a wrong move, one of the young men – and they were in my house – said: “If Allah came down from heaven and He came down here, you would never be able to make this move. If Allah Himself came here, you would never be able to make this move.” I stood up and said to him: “Do not say such words, shame on you!” He repeated the same words, so I said to him: “Now you are insisting on these words. Don’t come to my house again!” He said to me, “Okay,” and left the house. The guys said to me: “What you did is not right. The man was in your house, and you should not have treated him in this manner.” My anger was for the sake of Allah, may He be exalted. My question is: is it permissible for me to listen to people mocking Allah, may He be exalted, and not do something like what I did, and should I denounce it in my heart only, on the grounds that that is the weakest of faith? What is the ruling on one who utters such words and insists on that? What is your opinion of the way I reacted?
Praise be to Allah.Firstly:
These words that your friend uttered are very serious, and it is not appropriate for any Muslim to say such things. That constitutes disbelief (kufr) in Allah, may He be exalted, because of what it involves of disrespect towards Him, may He be exalted. Allah is able to move him and everything in this world, and to destroy him and all of humanity, with a single word (“Be!”), as He, may He be glorified and exalted, says (interpretation of the meaning):
{His command is only when He intends a thing that He says to it, "Be," and it is} [Yaa-Seen 36:82]
{They have certainly disbelieved who say that Allah is Christ, the son of Mary. Say, “Then who could prevent Allah at all if He had intended to destroy Christ, the son of Mary, or his mother or everyone on the earth?” And to Allah belongs the dominion of the heavens and the earth and whatever is between them. He creates what He wills, and Allah is over all things competent} [al-Maa’idah 5:17]
{And if you ask them, they will surely say, “We were only conversing and playing.” Say, “Is it Allah and His verses and His Messenger that you were mocking?" 
Make no excuse; you have disbelieved after your belief”} [at-Tawbah 9:65-66].
Secondly:
The one who uttered these words must repent to Allah, may He be exalted, and renew his faith by uttering the twin declaration of faith (ash-shahaadatayn) and affirming the greatness, majesty and might of Allah, may He be exalted. If he insists on what he said and does not repent from it, then he is a disbeliever and apostate who is beyond the bounds of Islam.
Thirdly:
We do not think that you did anything wrong in the way you reacted, because your denouncing evil is something that is obligatory, and the greatest of evils is reviling and mocking Allah, may He be exalted. So it is not permissible for the one who hears such a thing and is able to denounce it to remain silent; rather he is obliged to denounce it to the best of his ability, by taking action or speaking out. The Prophet ( blessings and peace of Allah be upon him) did not think it was acceptable for anyone to limit it to denouncing evil in his heart unless he was unable to change it by his actions or his words, as in the hadith in which the Prophet (blessings and peace of Allah be upon him) said: “Whoever among you sees an evil action, let him change it with his hand (by taking action); if he cannot, then with his tongue (by speaking out); and if he cannot, then with his heart (by hating it and feeling it is wrong), and that is the weakest of faith.” Narrated by Muslim (49).
It would have been better for your other friends to also denounce these words of falsehood and blatant disbelief, but lack of veneration for Allah, may He be exalted, in their hearts made them think little of these words of disrespect and disbelief in Him.
Yes, not throwing him out of your house may have been better, so that you could have given yourself the opportunity to argue with him in the way that is better, and call him to repent, regret his words and seek Allah’s forgiveness.
But this is insignificant in the face of the grave sin that your friend committed. How could people denounce a minor error and remain silent about a grievous sin?
Fourthly:
With regard to playing chess, if it distracts you from obligatory duties such as prayer and the like, or it involves anything haraam, such as lying or reviling and insulting others, and the like, then it is haraam according to the consensus of the scholars.
If it does not distract from any obligatory duty and is not accompanied by any haraam actions, then there is a difference of opinion concerning it. The majority of fuqaha’ – the Hanafis, Maalikis, Hanbalis and some of the Shaafa‘is – are of the view that it is haraam. This is what the Sahaabah stated in their fatwas. For more details regarding that, please see the answer to question no. 14095, which discusses how playing chess may lead to disbelief; we seek refuge with Allah from that.
So what you must do is give up playing this game and repent to Allah, may He be exalted, from that. We ask Allah to guide us and you, and to make us all steadfast in adhering to Islam.
And Allah knows best.