إِذْ يُوحِي رَبُّكَ إِلَى الْمَليِكَةِ أَنِّي مَعَكُمْ فَثَبِّتُواْ الَّذِينَ امَنُواْ
(Remember) when your Lord revealed to the angels, "Verily, I am with you, so keep firm those who have believed."
This is a hidden favor that Allah has made known to the believers, so that they thank Him and are grateful to Him for it. Allah, glorified, exalted, blessed and praised be He, has revealed to the angels -- whom He sent to support His Prophet, religion and believing group -- to make the believers firmer.
Allah's statement,
سَأُلْقِي فِي قُلُوبِ الَّذِينَ كَفَرُواْ الرَّعْبَ
I will cast terror into the hearts of those who have disbelieved.
means, `you -- angels -- support the believers, strengthen their (battle) front against their enemies, thus, implementing My command to you. I will cast fear, disgrace and humiliation over those who defied My command and denied My Messenger,
فَاضْرِبُواْ فَوْقَ الَاعْنَاقِ وَاضْرِبُواْ مِنْهُمْ كُلَّ بَنَانٍ
so strike them over the necks, and smite over all their fingers and toes.
strike them on their foreheads to tear them apart and over the necks to cut them off, and cut off their limbs, hands and feet.
According to Ad-Dahhak and Atiyyah Al-`Awfi,
فَوْقَ الَاعْنَاق
(over the necks), refers to striking the forehead, or the neck,
In support of the latter, Allah commanded the believers,
فَإِذَا لَقِيتُمُ الَّذِينَ كَفَرُواْ فَضَرْبَ الرِّقَابِ حَتَّى إِذَا أَثْخَنتُمُوهُمْ فَشُدُّواْ الْوَثَاقَ
So, when you meet (in fight Jihad in Allah's cause) those who disbelieve, smite (their) necks till when you have killed and wounded many of them, then bind a bond firmly (on them, take them as captives). (47;4)
Ar-Rabi bin Anas said,
"In the aftermath of Badr, the people used to recognize whomever the angels killed from those whom they killed, by the wounds over their necks, fingers and toes, because those parts had a mark as if they were branded by fire."
Allah said,
وَاضْرِبُواْ مِنْهُمْ كُلَّ بَنَانٍ
and smite over all their fingers and toes.
Ibn Jarir commented that this Ayah commands,
"O believers! Strike every limb and finger on the hands and feet of your (disbelieving) enemies."
Al-Awfi reported, that Ibn Abbas said about the battle of Badr that;
Abu Jahl said, "Do not kill them (the Muslims), but capture them so that you make known to them what they did, their ridiculing your religion and shunning Al-Lat and Al-Uzza (two idols)."
Allah than sent down to the angels,
أَنِّي مَعَكُمْ فَثَبِّتُواْ الَّذِينَ امَنُواْ
سَأُلْقِي فِي قُلُوبِ الَّذِينَ كَفَرُواْ الرَّعْبَ
فَاضْرِبُواْ فَوْقَ الَاعْنَاقِ وَاضْرِبُواْ مِنْهُمْ كُلَّ بَنَانٍ
Verily, I am with you, so keep firm those who have believed. I will cast terror into the hearts of those who have disbelieved, so strike them over the necks, and smite over all their fingers and toes.
In that battle, Abu Jahl (may Allah curse him) was killed along with sixty-nine men. `Uqbah bin Abu Mua`it was captured and then killed, thus bring the death toll of the pagans to seventy