Praise be to Allah.
Qiyaam al-layl is one of the best acts of worship that raise a person in status, increases good deeds, absolves his bad deeds, and brings him closer to the Lord of all creation. Praying qiyaam al-layl is encouraged in the book of Allah, may He be exalted, and in the Sunnah of His Prophet (blessings and peace of Allah be upon him).
For more information on that, please see the answer to question no. 50070.
We do not know of anything in the texts of the Quran or Sunnah to indicate that the angels look down from heaven on those who pray tahajjud at night, and could see them in their places on earth as the stars of the sky appear to the people of earth.
What is narrated from Ka‘b al-Ahbaar about him saying that “The angels look down from heaven upon those who pray tahajjud at night as you look at the stars of the sky” was mentioned by al-Haafiz Ibn Rajab in his book Ikhtiyaar al-Awlaa fi Sharh Hadith Ikhtisaam al-Malaa’ al-A‘laa (p. 91), where he said:
Karaz ibn Wabirah said: I heard that Ka‘b said: The angels look down from heaven upon those who pray tahajjud at night as you look at the stars of the sky.
This is not soundly narrated from Ka‘b, because the chain of narration is munqati‘ (interrupted); Karaz ibn Wabirah did not state who narrated that to him from Ka‘b; rather he conveyed it from Ka‘b (without mentioning the narrator in between).
Nothing is known about the status of Karaz ibn Wabirah as a narrator.
Even if we assume that the report is proven to be from Ka‘b, it does not prove anything, because Ka‘b was one of the Taabi‘een, one of the People of the Book who became Muslim, and he often quoted from the scriptures of the People of the Book, and that does not constitute proof.
Similarly, the words of Ibn al-Haaj in al-Madkhal (2/137): The angels see his place from heaven as the shining stars appear to us in the sky, do not count as evidence. The most that can be said concerning this is that he was narrating the meaning from Ka‘b.
Rather what counts as proof and evidence is the texts of the Quran and Sunnah.
Reciting Quran is light for a person, especially if he recites it in prayer. Imam Ahmad (11774) narrated from Abu Sa‘eed al-Khudri that a man came to him and said: Advise me. He said: I asked the Messenger of Allah (blessings and peace of Allah be upon him) for the same thing before you that you have asked me for, and he said: “I advise you to fear Allah, for that the foundation of everything. And you should strive in jihad, for it is the monasticism of Islam. You should remember Allah and recite the Quran, for it is your comfort in heaven, and will bring renown for you on earth.”
Classed as hasan by al-Albani in Saheeh al-Jaami‘ (2543).
Ibn Hibbaan narrated in his Saheeh (361) from Abu Dharr that the Prophet (blessings and peace of Allah be upon him) said: “You should recite the Quran and remember Allah, for that will be light for you on earth and will be stored up for you in heaven.”
Classed as hasan by al-Albani in Saheeh at-Targheeb (1422).
Al-Bayhaqi narrated in his Sunan (162) that ‘Ali (may Allah be pleased with him) said: We were instructed to use the siwaak and he [the Prophet (blessings and peace of Allah be upon him)] said: “When a person stands to pray, the angel comes to him and stands behind him, listening to the Quran and drawing closer, and he continues to listen and draw closer until he puts his mouth to his mouth, so he does not recite any verse but it goes inside the angel.”
Classed as saheeh by al-Albani in as-Saheehah (1213).
So prayer at night is light, and it is attended by the angels of mercy. This is proven. As for what is mentioned of the words of Ka‘b, there is no proof of that.
The time for praying qiyaam al-layl begins after ‘Isha’ prayer and lasts until the break of dawn. The best of it is the last third of the night.
The scholars of the Permanent Committee said:
The time for praying qiyaam al-layl and Witr is from after ‘Isha’ prayer until the break of dawn.
End quote from Fatawa al-Lajnah ad-Daa’imah (7/225).
Ibn Baaz (may Allah have mercy on him) said:
The time for tahajjud begins after ‘Isha’ and ends with the break of dawn. When the people have prayed ‘Isha’, the time for tahajjud begins and lasts until the break of dawn. The Sunnah is to pray qiyaam al-layl between the end of ‘Isha’ prayer and the break of dawn, even if it is one rak‘ah of Witr.
End quote from Fatawa Noor ‘ala ad-Darb (10/70).
Whatever prayer you offer after ‘Isha’ prayer comes under the heading of qiyaam al-layl. People vary in status in that regard, and their reward will vary according to how long they spend in qiyaam al-layl and other righteous deeds. Whoever prays two rak‘ahs after ‘Isha’, they are regarded as coming under the heading of qiyaam al-layl, but the one who prays two rak‘ahs and Witr after ‘Isha’ is not like one who gets up at night and prays as much as Allah wills that he should pray.
The reward and the virtue are commensurate with the level of the deed.
For more information on the difference between qiyaam al-layl and tahajjud, please see the answer to question no. 143240.
And Allah knows best.