Is the spoil (salb) of a slain enemy soldier granted to the killer in all circumstances?

Primary text

The spoil belongs to the killer in every situation, unless the enemy retreats. This is the position held by Al-Shafi'i, Abu Thawr, Dawud, and Ibn al-Mundhir. The evidence for this is the general statement of the Prophet, peace be upon him: "Whoever kills an enemy soldier, his is his spoil." Furthermore, the action of Abu Qatadah, who took the spoil of the man he killed, occurred during the clashing of the two armies, as indicated by his own description of engaging a polytheist attacking a Muslim. Similarly, the action of Abu Talha, who killed twenty men and took their spoils after the armies had engaged, supports this ruling.