وَنَقُولُ: «اللَّهُ أَعْلَمُ» فِيمَا اشْتَبَهَ عَلَيْنَا عِلْمُهُ
When the knowledge of something is uncertain to us, we say, “Allah knows best.”
Allahu a'lam expresses intellectual restraint. What is established by clear evidence is affirmed; where the reality or exact modality is beyond human knowledge, one does not pretend certainty but consigns the matter to Allah's knowledge.