8:19
إِن تَسْتَفْتِحُوا۟ فَقَدْ جَآءَكُمُ ٱلْفَتْحُ ۖ وَإِن تَنتَهُوا۟ فَهُوَ خَيْرٌ لَّكُمْ ۖ وَإِن تَعُودُوا۟ نَعُدْ وَلَن تُغْنِىَ عَنكُمْ فِئَتُكُمْ شَيْـًٔا وَلَوْ كَثُرَتْ وَأَنَّ ٱللَّهَ مَعَ ٱلْمُؤْمِنِينَ
If you [disbelievers] seek the victory - the defeat has come to you. And if you desist [from hostilities], it is best for you; but if you return [to war], We will return, and never will you be availed by your [large] company at all, even if it should increase; and [that is] because Allah is with the believers.
Context in Surah Al-Anfal
Nearby ayahs help place verse 8:19 in sequence and meaning.
فَلَمْ تَقْتُلُوهُمْ وَلَـٰكِنَّ ٱللَّهَ قَتَلَهُمْ ۚ وَمَا رَمَيْتَ إِذْ رَمَيْتَ وَلَـٰكِنَّ ٱللَّهَ رَمَىٰ ۚ وَلِيُبْلِىَ ٱلْمُؤْمِنِينَ مِنْهُ بَلَآءً حَسَنًا ۚ إِنَّ ٱللَّهَ سَمِيعٌ عَلِيمٌ
And you did not kill them, but it was Allah who killed them. And you threw not, [O Muhammad], when you threw, but it was Allah who threw that He might test the believers with a good test. Indeed, Allah is Hearing and Knowing.
ذَٰلِكُمْ وَأَنَّ ٱللَّهَ مُوهِنُ كَيْدِ ٱلْكَـٰفِرِينَ
That [is so], and [also] that Allah will weaken the plot of the disbelievers.
يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوٓا۟ أَطِيعُوا۟ ٱللَّهَ وَرَسُولَهُۥ وَلَا تَوَلَّوْا۟ عَنْهُ وَأَنتُمْ تَسْمَعُونَ
O you who have believed, obey Allah and His Messenger and do not turn from him while you hear [his order].
وَلَا تَكُونُوا۟ كَٱلَّذِينَ قَالُوا۟ سَمِعْنَا وَهُمْ لَا يَسْمَعُونَ
And do not be like those who say, "We have heard," while they do not hear.