ولا قصاص على الشاهد في مسألة شهود القصاص إذا رجعوا؛ لأنه ليس بقتال
When witnesses withdraw testimony in a retaliation case, the witness is not himself subjected to retaliation, for he did not commit the killing.
Here the specific legal consequence of retaliation is tied to the attribution of the relevant killing. Other possible effects of testimony or its withdrawal are separate matters; giving testimony is not identical to performing the killing.
As in the usurpation case, the point is to distinguish the cause required for a specified ruling from all possible consequences of the wider event.