These three I think are the greatest most performed sins in our generation now. Allah has said it best in the following verses of the Quran, so I will just post them here.
“And if it had not been for the favor of Allah upon you and His mercy in this world and the Hereafter, you would have been touched for that [lie] in which you were involved by a great punishment * When you received it with your tongues and said with your mouths that of which you had no knowledge and thought it was insignificant while it was, in the sight of Allah , tremendous. * And why, when you heard it, did you not say, “It is not for us to speak of this. Exalted are You, [O Allah ]; this is a great slander”? * Allah warns you against returning to the likes of this [conduct], ever, if you should be believers. “ Surah 24: 14 – 17
“Indeed, those who [falsely] accuse chaste, unaware and believing women are cursed in this world and the Hereafter; and they will have a great punishment “ Surah 24: 23
“O you who have believed, let not a people ridicule [another] people; perhaps they may be better than them; nor let women ridicule [other] women; perhaps they may be better than them. And do not insult one another and do not call each other by [offensive] nicknames. Wretched is the name of disobedience after [one’s] faith. And whoever does not repent – then it is those who are the wrongdoers. * O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin. And do not spy or backbite each other. Would one of you like to eat the flesh of his brother when dead? You would detest it. And fear Allah ; indeed, Allah is Accepting of repentance and Merciful. “ Surah 49: 11 – 12
“Abu Huraira reported Allah’s Messenger (may peace be upon him) as saying: Do you know what is backbiting? They (the Companions) said: Allah and His Messenger know best. Thereupon he (the Holy Prophet) said: Backbiting implies your talking about your brother in a manner which he does not like. It was said to him: What is your opinion about this that if I actually find (that failing) in my brother which I made a mention of? He said: If (that failing) is actually found (in him) what you assert, you in fact have backbitten him, and if that is not in him it is a slander. “[Sahih Muslim Book 32, #6265]