Sura 48 Al-Fath (The Victory), aya 18

1. لَقَدْ رَضِيَ اللَّهُ عَنِ الْمُؤْمِنِينَ إِذْ يُبَايِعُونَكَ تَحْتَ الشَّجَرَةِ فَعَلِمَ مَا فِي قُلُوبِهِمْ فَأَنْزَلَ السَّكِينَةَ عَلَيْهِمْ وَأَثَابَهُمْ فَتْحًا قَرِيبًا

   Certainly was Allah pleased with the believers when they pledged allegiance to you, (O Muhammad), under the tree, and He knew what was in their hearts, so He sent down tranquillity upon them and rewarded them with an imminent conquest

   48:18

Tafsiri: Saheeh International