مَا أَنتَ إِلاَّ بَشَرٌ مِّثْلُنَا
You are but a human being like us.
meaning, `how can you receive Revelation when we do not!'
This is like the Ayah where they are described as saying;
أَءُلْقِىَ الذِّكْرُ عَلَيْهِ مِن بَيْنِنَا بَلْ هُوَ كَذَّابٌ أَشِرٌ
سَيَعْلَمُونَ غَداً مَّنِ الْكَذَّابُ الاٌّشِرُ
"Is it that the Reminder is sent to him alone from among us! Nay, he is an insolent liar!"
Tomorrow they will come to know who is the liar, the insolent one! (54;26-27)
فَأْتِ بِأيَةٍ إِن كُنتَ مِنَ الصَّادِقِينَ
Then bring us a sign if you are of the truthful.
Then they asked him for a sign to prove that what he brought to them from their Lord was the truth. A crowd of them gathered and demanded that he immediately bring forth from the rock a she-camel that was ten months pregnant, and they pointed to a certain rock in their midst.
Allah's Prophet Salih made them promise that if he responded to their request, they would believe in him and follow him. So they agreed to that.
The Prophet of Allah Salih, peace be upon him, stood and prayed, then he prayed to Allah to grant them their request. Then the rock to which they had pointed split open, revealing a she-camel that was ten months pregnant, exactly as they had requested.
So some of them believed, but most of them disbelieved.
قَالَ هَذِهِ نَاقَةٌ لَّهَا شِرْبٌ وَلَكُمْ شِرْبُ يَوْمٍ مَّعْلُومٍ