Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, was told, “O Messenger of Allah, pray against the idolaters!” So the Prophet said:
إِنِّي لَمْ أُبْعَثْ لَعَّانًا وَإِنَّمَا بُعِثْتُ رَحْمَةً
Verily, I was not sent to invoke curses, but rather I was only sent as a mercy.
Source: Sahih Muslim 2599, Grade: Sahih
Source: Sahih Muslim 2595, Grade: Sahih

Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said:
لَا يَنْبَغِي لِصِدِّيقٍ أَنْ يَكُونَ لَعَّانًا
It is not befitting the truthful that they curse others.
Anas ibn Malik reported:
لَمْ يَكُنْ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ سَبَّابًا وَلَا فَحَّاشًا وَلَا لَعَّانًا كَانَ يَقُولُ لِأَحَدِنَا عِنْدَ الْمَعْتِبَةِ مَا لَهُ تَرِبَ جَبِينُهُ
The Prophet, peace and blessings be upon him, would not abuse others, he would not use obscene words, and he would not curse others. If he wanted to admonish anyone of us, he used to say: What is wrong with him? His forehead be dusted!
Source: Sahih Bukhari 5684, Grade: Sahih