Glad Tidings: Signs of Defeat for those who Insult Allah’s Messenger.
Ibn Taymiyah says “Many Muslims, trust worthy, people of expertise and Fiqh spoke many times about their experiences when they surrounded castles and cities in Sham and surrounded the Christians.
They said we would surround the castle or the city, for a month or more and our besieging of them is doing nothing, and we are almost going to give up and leave. Then when the people of that town or castle, would start cursing the Messenger of Allah (peace and blessings of Allah be upon him) suddenly it would fall in our hands, sometimes the delay would not be even a day or two and it would be opened by force. So we would take it as a glad tiding when we would hear them curse the Messenger of Allah (peace and blessings of Allah be upon him) even though our hearts would be filled with hatred but we would see it as a glad tiding because it is a sign of our coming victory.”
And that is the meaning of the ayah in Surah al Kawthar:
إِنَّ شَانِئَكَ هُوَ الاٌّبْتَرُ
“Indeed your enemy is the one who is cutoff!“
[Surah al Kawthar 108:3]
So Allah Almighty will cutoff the enemies of Muhammad (peace and blessings of Allah be upon him).