What does the word acceptance (qubūl) mean?
In the name of God, The Most Merciful, The Especially Merciful.
The Prophet (Peace Be Upon Him) said: “Prayer (ṣalāt) will not be accepted without purification, nor charity from treacherous dealings”
This means that without being in a state of purity one cannot perform the prayer nor will it be accepted. However, if one gives charity from wealth acquired through impermissible means, whilst this may be accepted, there will be no reward for this act.
The question then is, why is there a difference in the actual application of the word acceptance (qubūl) for the two acts?
This comes down to how the word acceptance is applied. In Arabic, it has two secondary two meanings; one is in relation to the act being complete and correct (ṣiḥaḥ) with the conditions for the completion of that act being present. The other meaning is that the pleasure of God Almighty is acquired (riḍā) and the promise of reward.
So when we come across the word acceptance we need to understand which one of the two secondary meanings are applicable. The following two narrations will make this clearer:
“God does not accept the prayer of an adult woman unless she wears a head covering (khimār)”
Here the word acceptance refers to the prayer being complete and correct. In other words, without the head covering the prayer is incomplete.
“Whoever goes to a fortuneteller and asks him about something, his prayer will not be accepted for forty days.” (Muslim)
Here the word acceptance refers to the pleasure of God Almighty being acquired. In other words, whilst the act has been completed and the person is still required to pray, the pleasure of God Almighty has not been acquired and so there is no reward.
So from the opening narration it becomes clear that the first part refers to the prayer being complete and the second part refers to the fact that charity has not being accepted in terms of God Almighty not being pleased with the act. In other words, we find in this narration one word (i.e. acceptance) but the application is very different.
This is why a firm understanding of Arabic is required to save us from making errors when it comes to Islamic law.
And God knows best.
 In any case, such money acquired through impermissible means should be given away to charity without any hope of reward.