وَقَالَ لَهُمْ نَبِيُّهُمْ إِنَّ ءَايَةَ مُلْكِهِۦٓ أَن يَأْتِيَكُمُ ٱلتَّابُوتُ فِيهِ سَكِينَةٌ مِّن رَّبِّكُمْ وَبَقِيَّةٌ مِّمَّا تَرَكَ ءَالُ مُوسَىٰ وَءَالُ هَـٰرُونَ تَحْمِلُهُ ٱلْمَلَـٰٓئِكَةُ ۚ إِنَّ فِى ذَٰلِكَ لَـَٔايَةً لَّكُمْ إِن كُنتُم مُّؤْمِنِينَ
Their prophet further said to them: “The sign of his kingship is that the Ark will come to you – carried by the angels – having therein tranquility[138] from your Lord and remains of what the House of Moses and the House of Aaron had left. Indeed, there is a sign in this for you, if you are true believers.”
Their prophet said to them that the mark of his being truly chosen as their king was that Allah would return to them the Ark. This was a chest revered by the Israelites which was taken away from them. In it there was tranquillity and relics left behind by the family of Moses and Aaron, such as the staff and a few tablets. In that there is a clear sign if you are true believers.