For a much better (i.e. more accurate) rendition I recommend:
source17)
fa darba al rriqabi hattaitha athkhantumoohum = so strike the necks until when you have overcome them
[47:4]
Some use "hit", "smite", "strike-off". Whilst this is the most common translation, it should be noted that it is taken by many as an idiom (e.g. Al-Jalalayn, Ibn Kathir), meaning slay or kill. This seems a plausible interpretation as in a battle of swords and arrows no commander would order his soldiers to aim for the necks alone. Similarly, "put forth" could also be used. Interestingly, Mustansir Mir's book mentions a similar expression "daraba raqabatahu" and renders it as "to cut off somebody's head / kill somebody".
However, upon closer examination, there is an alternative translation, which seems the most likely based on the evidence:
So, when you encounter those who have rejected/concealed, then put forth /bring about the captives; until when you have subdued/overcome them, then strengthen the bind. Then after either grace/favour or ransom, until the war lays down its burdens. That, and had God willed, surely He would have gained victory Himself from them, but He tests some of you with others. And those who get killed in the cause of God, He will never let their deeds be put to waste.Notes for the above translation:
1) "darba" is a verbal noun, indicating the act of doing as well as the noun itself, e.g. then putting forth / bringing about the captives.
2) In a battle of swords and arrows no commander would order his soldiers to aim for the necks alone.
3) RQB is NEVER used to mean neck elsewhere in The Quran, as the word for neck is "unuq" (as used in 8:12 also with DRB). RQB is always used to mean slaves/captives.
4) If they were supposed to be beheaded, there would not be a need for an instruction regarding captives. Thus to overcome this apparent omission, many traditional commentators translate "fa shuddoo al wathaqa" as "then tie the bond" and say this refers to taking prisoners of war. However, the word "strengthen/tighten (Arabic: shuddoo)" implies a pre-existing thing to strengthen/tighten (see its usage in 38:20, 76:28, 28:35, 10:88, 20:31), but if this is true, where is it in context? It can only relate to "darba al rriqabi", and thus provides strong proof that this phrase is about bringing about captives from the enemy.
5) This translation makes sense because during open/active fighting, the captives may not be totally secure, and could only really be secured once the enemy has been subdued/overcome. Thus, this verse is implying aim to bring about captives, not necessarily kill them, which shows mercy and less aggression in such a situation, even if it means getting killed.
6) One meaning of DaRaBa found in Lane's Lexicon is "he made or caused to be or constituted" which is similar to the suggested meaning discussed above.
7) I am not aware of a Classical Arabic Dictionary which references verse 47:4 under the root entry of DRB or RQB.
47:4 refers to those mentioned in the previous verses, going by its use of connective particle "fa", then these people were not fighting or killing, thus killing them may violate the law of equivalence [2:190, 4:90, 5:8, 16:126, 42:39-43].
9) Interestingly, Traditional Tafsirs (altafsir.com) also mention this possibility along with the common understanding. Ibn 'Abbas: "...and taken them prisoners, (then making fast of bonds) keep the prisoners in captivity...". Tafsir al-Jalalayn: "...take them captive and bind firmly, the bonds (al-wathāq is what is used to bind [yūthaqu] a captive).".