Ma'arif al-Qur'an
Mufti Muhammad ShafiVerse 249: قَالَ إِنَّ اللَّـهَ مُبْتَلِيكُم بِنَهَرٍ (He said: Allah is going to test you by ariver).
The wisdom behind this test, as perceived by this humble commentator, appears to be as follows. Not difficult to imagine is the excitement created on such occasions but there are not many who would stay firm in their hour of trial. And should such a time come, the weakness shown by such people becomes contagious making others panic as well. Allah Almighty willed that such people be pruned out. This purpose was accomplished by this test, which is very appropriate, because steadfastness is necessary in fighting. So, being patient, when water is made available without asking in a state of intense thirst, is a proof of steadfastness, and dashing for water is a proof of its absence. Later on comes the unusual: Those who drank too much water became mysteriously more incapacitated. This has appeared in Ruh al-Ma'ani on the authority of Ibn Abi Haim from Ibn ` Abbas ؓ .
Now the events and sayings mentioned in this story tell us that there were three kinds of people among them:(1) The weak in faith who failed to make the grade in their hour oftrial.(2) The perfect who fully succeeded in their trial but did feel concerned about how low they were in numbers.(3) The most perfect who did not bother even about that.