قَالُوا اطَّيَّرْنَا بِكَ وَبِمَن مَّعَكَ
"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 جَأءَتْهُمُ الْحَسَنَةُ قَالُواْ لَنَا هَـذِهِ وَإِن تُصِبْهُمْ سَيِّيَةٌ يَطَّيَّرُواْ بِمُوسَى وَمَن مَّعَهُ
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;
وَإِن تُصِبْهُمْ حَسَنَةٌ يَقُولُواْ هَـذِهِ مِنْ عِندِ اللَّهِ وَإِن تُصِبْهُمْ سَيِّيَةٌ يَقُولُواْ هَـذِهِ مِنْ عِندِكَ قُلْ كُلٌّ مِّنْ عِندِ 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;
قَالُواْ إِنَّا تَطَيَّرْنَا بِكُمْ لَيِن لَّمْ تَنتَهُواْ لَنَرْجُمَنَّكُمْ وَلَيَمَسَّنَّكُمْ مِّنَّا عَذَابٌ أَلِيمٌ
قَالُواْ طَـيِرُكُم مَّعَكُمْ
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 وَبِمَن مَّعَكَ قَالَ طَايِرُكُمْ عِندَ 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 أَنتُمْ 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