And indeed he saw him in the clear horizon.
meaning, indeed Muhammad saw Jibril, who brought him the Message from Allah, in the form that Allah created him in (i.e., his true form), and he had six hundred wings.
بِالاْاُفُقِ الْمُبِينِ
in the clear horizon.
meaning, clear.
This refers to the first sighting which occurred at Al-Batha' (Makkah). This incident is mentioned in Allah's statement,
عَلَّمَهُ شَدِيدُ الْقُوَى
ذُو مِرَّةٍ فَاسْتَوَى
وَهُوَ بِالاٍّفُقِ الاٌّعْلَى
ثُمَّ دَنَا فَتَدَلَّى
فَكَانَ قَابَ قَوْسَيْنِ أَوْ أَدْنَى
فَأَوْحَى إِلَى عَبْدِهِ مَأ أَوْحَى
He has been taught by one mighty in power (Jibril).
Dhu Mirrah, then he rose.
While he was in the highest part of the horizon.
Then he approached and came closer.
And was at a distance of two bows' length or less.
So (Allah) revealed to His servant what He revealed. (53;5-10)
The explanation of this and its confirmation has already preceded, as well as the evidence that proves that it is referring to Jibril. It seems apparent -- and Allah knows best -- that this Surah (At-Takwir) was revealed before the Night Journey (Al-Isra'), because nothing has been mentioned in it except this sighting (of Jibril), and it is the first sighting.
The second sighting has been mentioned in Allah's statement,
وَلَقَدْ رَءَاهُ نَزْلَةً أُخْرَى
عِندَ سِدْرَةِ الْمُنتَهَى
عِندَهَا جَنَّةُ الْمَأْوَى
إِذْ يَغْشَى السِّدْرَةَ مَا يَغْشَى
And indeed he saw him (Jibril) at a second descent.
Near Sidrah Al-Muntaha.
Near it is the Paradise of Abode.
When that covered the lote tree which did cover it ! (53;13-16)
And these Ayat have only been mentioned in Surah An-Najm, which was revealed after Surah Al-Isra'(The Night Journey).
وَمَا هُوَ عَلَى الْغَيْبِ بِضَنِينٍ