or is there something else that is opposite or similar to it...
From all the teachings i have received the rule I'd say is Islamic is do what's the best. Basically people change so labelling someone as sinner may make us overlook his/her good parts and overlook their change if it occurs.
Please provide hadiths/Quran if possible
“Hate the sin, not the sinner” is only partly correct in Islam. Only a sinner with sins wholly occupying his heart making his heart dark lacking any light spot survived in it is one we should hate and even curse against them, though, if we can identify them correctly. About any other sinner no we cannot hate himself, but we must hate the sin, and the majority of the sinners belong to this latter group. The former group are those who would be left in the hell eternally, the rest will be survived from the hell and let enter the heaven after centuries and maybe millenniums or more of being tortured in the hell.
Those with completely dark hearts will never find the opportunity to repent in Dunya (world), they are Taqut (طاغوت: or leaders inviting to the Fire: أَئِمَّةً يَدْعُونَ إِلَى النَّارِ, Al-Qasas,41) against which Allah has ordered us to be Kafir about them. The others we should always have hope that they may repent, and we should help them so by enjoying them to what is right and banning them from what s wrong.
اللَّـهُ وَلِيُّ الَّذِينَ آمَنُوا يُخْرِجُهُم مِّنَ الظُّلُمَاتِ إِلَى النُّورِ ۖ وَالَّذِينَ كَفَرُوا أَوْلِيَاؤُهُمُ الطَّاغُوتُ يُخْرِجُونَهُم مِّنَ النُّورِ إِلَى الظُّلُمَاتِ ۗ أُولَـٰئِكَ أَصْحَابُ النَّارِ ۖ هُمْ فِيهَا خَالِدُونَ
Allah is the ally of those who believe. He brings them out from darknesses into the light. And those who disbelieve - their allies are Taghut. They take them out of the light into darknesses. Those are the companions of the Fire; they will abide eternally therein. [Al-Baqareh, 257]
Godspeed
It depends on the type of sin.
Quran says there has already been for you an excellent pattern in Abraham. So this means that we should follow this pattern. He many times invited his people to monotheism by kindness. But they still insisted on Shirk and did not leave their idols and tried to kill prophet Ibrahim a.s.
A Muslims should disassociate and have animosity and hatred about Mushrik people (those who worship other than Allah like idol, Satan...). But hating is some different. We can disassociate one but still love him for guidance.
There has already been for you an excellent pattern in Abraham and those with him, when they said to their people, "Indeed, we are disassociated from you and from whatever you worship other than Allah. We have denied you, and there has appeared between us and you animosity and hatred forever until you believe in Allah alone" except for the saying of Abraham to his father, "I will surely ask forgiveness for you, but I have not [power to do] for you anything against Allah. Our Lord, upon You we have relied, and to You we have returned, and to You is the destination. http://tanzil.net/#60:4
Prophet Muhammad SAWW did so also. he invited people many times and many of them accepted but some still did not accept and tried to kill prophet and made wars like Badr, Uhod and other wars and tried to kill Muslims. so then prophet made around 100 wars against them (although himself did not participate in all of them directly).
But it is important to distinguish between clear Shirk and Hidden Shirk. This applies only to clear Shirk. Because many of believers have hidden shirk:
And most of them believe not in Allah except while they associate others with Him. http://tanzil.net/#12:106
But a Muslim who believes in Allah but still is sinner is different.
There has certainly come to you a Messenger from among yourselves. Grievous to him is what you suffer; [he is] concerned over you and to the believers is kind and merciful. http://tanzil.net/#9:128
We should love and guide Muslims who are going astray and are sinner.
