And indeed We sent to Thamud their brother Salih, (saying): "Worship Allah." Then look! They became two parties quarreling with each other (45)He said: "O my people! Why do you seek to hasten the evil before the good Why seek you not the forgiveness of Allah, that you may receive mercy? (46)They said: "We augur an omen from you and those with you." He said: "Your omen is of Allah; nay, but you are a people that are being tested. (47)

Allah tells us about Thamud and how they responded to their Prophet Salih, when Allah sent him to call them to worship Allah alone, with no partner or associate.

فَإِذَا هُمْ فَرِيقَانِ يَخْتَصِمُونَ

(Then look! They became two parties quarreling with each other.)

Mujahid said, "These were believers and disbelievers." This is like the Ayah,

قَالَ الْمَلَأُ الَّذِينَ اسْتَكْبَرُوا مِنْ قَوْمِهِ لِلَّذِينَ اسْتُضْعِفُوا لِمَنْ آمَنَ مِنْهُمْ أَتَعْلَمُونَ أَنَّ صَالِحًا مُرْسَلٌ مِنْ رَبِّهِ ۚ قَالُوا إِنَّا بِمَا أُرْسِلَ بِهِ مُؤْمِنُونَ - قَالَ الَّذِينَ اسْتَكْبَرُوا إِنَّا بِالَّذِي آمَنْتُمْ بِهِ كَافِرُونَ

(The leaders of those who were arrogant among his people said to those who were counted weak – to such of them as believed: "Know you that Salih is one sent from his Lord." They said: "We indeed believe in that with which he has been sent." Those who were arrogant said: "Verily, we disbelieve in that which you believe in.")(7:75-76)

قَالَ يَا قَوْمِ لِمَ تَسْتَعْجِلُونَ بِالسَّيِّئَةِ قَبْلَ الْحَسَنَةِ ۖ 

(He said: "O my people! Why do you seek to hasten the evil before the good?") meaning, 'why are you praying for the punishment to come, and not asking Allah for His mercy?' Then he said:

لَوْلَا تَسْتَغْفِرُونَ اللَّهَ لَعَلَّكُمْ تُرْحَمُونَ - قَالُوا اطَّيَّرْنَا بِكَ وَبِمَنْ مَعَكَ ۚ

("Why seek you not the forgiveness of Allah, that you may receive mercy?" They said: "We augur an omen from you and those with you.")

This means: "We do not see any good in your face and the faces of those who are following you." Since they were doomed, whenever anything bad happened to any of them they would say, "This is because of Salih and his companions." Mujahid said, "They regarded them as bad omens." This is similar to what Allah said about the people of Fir'awn:

فَإِذَا جَاءَتْهُمُ الْحَسَنَةُ قَالُوا لَنَا هَٰذِهِ ۖ وَإِنْ تُصِبْهُمْ سَيِّئَةٌ يَطَّيَّرُوا بِمُوسَىٰ وَمَنْ مَعَهُ ۗ

(But whenever good came to them, they said: "Ours is this." And if evil afflicted them, they saw it as an omen about Musa and those with him)(7:131). And Allah says:

وَإِنْ تُصِبْهُمْ حَسَنَةٌ يَقُولُوا هَٰذِهِ مِنْ عِنْدِ اللَّهِ ۖ وَإِنْ تُصِبْهُمْ سَيِّئَةٌ يَقُولُوا هَٰذِهِ مِنْ عِنْدِكَ ۚ قُلْ كُلٌّ مِنْ عِنْدِ اللَّهِ ۖ 

(And if some good reaches them, they say, "This is from Allah," but if some evil befalls them, they say, "This is from you." Say: "All things are from Allah.")(4:78) i.e., by virtue of His will and decree.

And Allah tells us about the dwellers of the town, when the Messengers came to them:

قَالُوا إِنَّا تَطَيَّرْنَا بِكُمْ ۖ لَئِنْ لَمْ تَنْتَهُوا لَنَرْجُمَنَّكُمْ وَلَيَمَسَّنَّكُمْ مِنَّا عَذَابٌ أَلِيمٌ - قَالُوا طَائِرُكُمْ مَعَكُمْ ۚ 

(They (people) said: "For us, we see an omen from you; if you cease not, we will surely stone you, and a painful torment will touch you from us." They (Messengers) said: "Your omens are with yourselves!)(36:18)

And these people [Thamud] said:

اطَّيَّرْنَا بِكَ وَبِمَنْ مَعَكَ ۚ قَالَ طَائِرُكُمْ عِنْدَ اللَّهِ ۖ 

("We augur an omen from you and those with you." He said: "Your omen is of Allah;) meaning, Allah will punish you for that.

بَلْ أَنْتُمْ قَوْمٌ تُفْتَنُونَ

(nay, but you are a people that are being tested.)

Qatadah said: "You are being tested to see whether you will obey or disobey." The apparent meaning of the phrase

تُفْتَنُونَ

(are being tested) is: you will be left to get carried away in your state of misguidance.