﴿ ۞ لَّقَدْ رَضِىَ ٱللَّهُ عَنِ ٱلْمُؤْمِنِينَ إِذْ يُبَايِعُونَكَ تَحْتَ ٱلشَّجَرَةِ فَعَلِمَ مَا فِى قُلُوبِهِمْ فَأَنزَلَ ٱلسَّكِينَةَ عَلَيْهِمْ وَأَثَٰبَهُمْ فَتْحًۭا قَرِيبًۭا ﴾

“INDEED, well-pleased was God with the believers when they pledged their allegiance unto thee [O Muhammad] under that tree, for He knew what was in their hearts; and so He bestowed inner peace upon them from on high, and rewarded them with [the glad tiding of] a victory soon to come”

Please check ayah 48:19 for complete tafsir.