But it will be only a single Zajrah. When behold, they are at As-Sahirah.
meaning, this is a matter that is from Allah that will not occur twice, nor will there be any opportunity to affirm it or verify it. The people will be standing and looking. This will be when Allah commands the angel Israfil to blow into the Sur, which will be the blowing of the resurrection. At that time the first people and the last people will all be standing before their Lord looking.
This is as Allah says,
يَوْمَ يَدْعُوكُمْ فَتَسْتَجِيبُونَ بِحَمْدِهِ وَتَظُنُّونَ إِن لَّبِثْتُمْ إِلاَّ قَلِيلً
On the Day when He will call you, and you will answer with His praise and obedience, and you will think that you have stayed but a little while! (17;52)
Allah has also said,
وَمَأ أَمْرُنَأ إِلاَّ وَحِدَةٌ كَلَمْحٍ بِالْبَصَرِ
And our commandment is but one as the twinkling of an eye. (54;50)
Allah also says,
وَمَأ أَمْرُ السَّاعَةِ إِلاَّ كَلَمْحِ الْبَصَرِ أَوْ هُوَ أَقْرَبُ
And the matter of the Hour is not but as a twinkling of the eye, or even nearer. (16;77)
Allah then says,
فَإِذَا هُم بِالسَّاهِرَةِ
When behold, they are at As-Sahirah.
Ibn Abbas said, "As-Sahirah means the entire earth."
Sa`id bin Jubayr, Qatadah and Abu Salih have all said this as well.
Ikrimah, Al-Hasan, Ad-Dahhak, and Ibn Zayd have all said,
"As-Sahirah means the face of the earth."
Mujahid said,
"They will be at its (the earth's) lowest part, and they will be brought out to highest part."
Then he said, "As-Sahirah is a level place."
Ar-Rabi` bin Anas said,
فَإِذَا هُم بِالسَّاهِرَةِ
When behold, they are at As-Sahirah. "Allah says,
يَوْمَ تُبَدَّلُ الاٌّرْضُ غَيْرَ الاٌّرْضِ وَالسَّمَـوَتُ وَبَرَزُواْ للَّهِ الْوَاحِدِ الْقَهَّارِ
On the Day when the earth will be changed to another earth and so will be the heavens, and they will appear before Allah, the One, the Irresistible. (14;48)
and He says,
وَيَسْـَلُونَكَ عَنِ الْجِبَالِ فَقُلْ يَنسِفُهَا رَبِّى نَسْفاً
فَيَذَرُهَا قَاعاً صَفْصَفاً
لااَّ تَرَى فِيهَا عِوَجاً وَلاا أَمْتاً
And they ask you concerning the mountains;
say,
"My Lord will blast them and scatter them as particles of dust.
Then He shall leave them as a level smooth plain.
You will see therein nothing crooked or curved. (20;105-107)
and Allah says,
وَيَوْمَ نُسَيِّرُ الْجِبَالَ وَتَرَى الاٌّرْضَ بَارِزَةً
And the Day We shall cause the mountains to pass away, and you will see the earth as a leveled plain. (18;47)
and the earth will be brought forth which will have mountains upon it, and it will not be considered from this earth (of this life). It will be an earth that no sin will be performed on it, nor will any blood be shed upon it.'