Surah At-Tawbah 9:40

إِلَّا تَنصُرُوهُ فَقَدْ نَصَرَهُ ٱللَّهُ إِذْ أَخْرَجَهُ ٱلَّذِينَ كَفَرُوا۟ ثَانِىَ ٱثْنَيْنِ إِذْ هُمَا فِى ٱلْغَارِ إِذْ يَقُولُ لِصَـٰحِبِهِۦ لَا تَحْزَنْ إِنَّ ٱللَّهَ مَعَنَا ۖ فَأَنزَلَ ٱللَّهُ سَكِينَتَهُۥ عَلَيْهِ وَأَيَّدَهُۥ بِجُنُودٍ لَّمْ تَرَوْهَا وَجَعَلَ كَلِمَةَ ٱلَّذِينَ كَفَرُوا۟ ٱلسُّفْلَىٰ ۗ وَكَلِمَةُ ٱللَّهِ هِىَ ٱلْعُلْيَا ۗ وَٱللَّهُ عَزِيزٌ حَكِيمٌ

If you do not aid him [i.e., the Prophet (ﷺ)] - Allāh has already aided him when those who disbelieved had driven him out [of Makkah] as one of two, when they were in the cave and he [i.e., Muḥammad (ﷺ)] said to his companion, "Do not grieve; indeed Allāh is with us." And Allāh sent down His tranquility upon him and supported him with soldiers [i.e., angels] you did not see and made the word of those who disbelieved the lowest, while the word of Allāh - that is the highest. And Allāh is Exalted in Might and Wise.

Translation: Saheeh International

Tafsir

If you do not help him that is the Prophet s know that God has already helped him when the disbelievers drove him forth from Mecca that is they made him resort to leaving when they desired to kill him or imprison him or banish him at the council assembly — the second of two thāniya ithnayn this is a circumstantial …

Excerpt from Tafsir al-Jalalayn, commentary on 9:40, via Quran.com. The reader has the full commentary and 9 more tafsirs.