Saʿd's vow after the Trench
He thought the fighting was over and made a condition.
اللَّهُمَّ إِنَّكَ تَعْلَمُ أَنَّهُ لَيْسَ أَحَدٌ أَحَبَّ إِلَىَّ أَنْ أُجَاهِدَهُمْ فِيكَ مِنْ قَوْمٍ كَذَّبُوا رَسُولَكَ صلى الله عليه وسلم وَأَخْرَجُوهُ
Allāhumma innaka taʿlamu annahu laysa aḥadun aḥabba ilayya an ujāhidahum fīka min qawmin kadhdhabū rasūlaka wa akhrajūh
“O Allah, You know there is no one I would rather strive against for Your sake than a people who called Your Messenger a liar and drove him out.”
Where this comes from
Aisha reports it. He had taken an arrow at the Trench. He said this, and then: O Allah, I think You have ended the war between us and them. And he asked that if any of it was left, he be kept alive for it.
The full narration
Narrated Aisha:Sa`d said, "O Allah! You know that there is none against whom I am eager to fight more willingly for Your Cause than those people who disbelieved Your Apostle and drove him out (of his city). O Allah! I think that You have ended the fight between us and them
Source
Ṣaḥīḥ al-Bukhārī · 3901
- Agreed upon as authentic (al-Bukhārī / Muslim)