ٱلسَّلَامُ عَلَيْكُمْ وَرَحْمَةُ ٱللَّٰهِ وَبَرَكَاتُهُ أَحْسَنَ ٱللَّٰهُ إِلَيْكُمْ Is sending la'an (curse) on someone takfeer?

Sending a curse upon somebody is that you are casting them out from the mercy of Allah, and the Muslim should never accustom himself to such things. The Messenger of Allah was not like this; he was not a la'an (a person who curses). He is a role model, and we should follow him.