In the third verse (89), it was said that the prayer of Sayyidna Musa (علیہ السلام) has been accepted. But, by taking Sayyidna Harun (علیہ السلام) as associated with the act of prayer, the actual address was made in the words: قَدْ أُجِيبَت دَّعْوَتُكُمَا (The prayer of you both has been granted). There was a reason for it. When Sayyidna Musa (علیہ السلام) السلام was making this prayer, Sayyidna Harun (علیہ السلام) kept saying Amin (Amen). This tells us that the saying of Amin آمِین (so be it) is also a part of the prayer itself. And since the masnun method of du` a or prayer given in the Holy Qur'an is that of making it in a lowered voice, the saying of آمِین Amin too in a lowered mode seems to be preferable.
As for the acceptance of prayer, the information was given to the two prophets as it appears in this verse. But, even they were some-what tested in that the effect of the prayer, according to al-Baghawi, unfolded after forty years. For this reason, soon after the mention of the acceptance of their prayer in this verse, they both were given the instruction: فَاسْتَقِيمَا وَلَا تَتَّبِعَانِّ سَبِيلَ الَّذِينَ لَا يَعْلَمُونَ (so stand firm, and never follow the way of those who do not know). It means that they should go on carrying the mission of calling people to the true faith and do not get embarrassed, disappointed or hasty like the ignorant when the effects of the acceptance of some prayer takes its due time.