Praise be to Allah.
The phrase al-mala al-a’ala is mentioned in both the Quran and the sunnah (prophetic teachings).
In Surah Saad, Allah says (interpretation of the meaning):
"‘I had no knowledge of the chiefs (angels) on high when they were disputing and discussing (about the creation of Adam). Only this has been inspired to me, that I am a plain warner.’" [38:69-70]
In his commentary on this ayah (verse), Shaykh al-Mufassireen Ibn Jareer al-Tabari (may Allah have mercy on him) said: "‘I had no knowledge of the chiefs on high (al-mala al-a’ala) when they were disputing and discussing’: here Allah is telling His Prophet Muhammad (peace and blessings of Allah be upon him) , ‘O Muhammad, say to the mushrikeen (polytheists) among your people: "I had no knowledge of the chiefs (angels) on high when they were disputing and discussing" about the creation of Adam before Allah revealed this to me.’ What this means is: ‘My telling you about this is clear proof that this Quran is a Revelation from Allah, because you know that I had no knowledge of this before this Quran was revealed; it is not something I witnessed with my own two eyes – I know it only because Allah has informed me of it.’"
Other scholars of tafseer (exegesis) have said something similar to this.
The comments of other scholars:
Ibn ‘Abbas (may Allah be pleased with him and his father) said: "Allah’s words (interpretation of the meaning) ‘I had no knowledge of the chiefs on high when they were disputing and discussing’ refer to the angels, when they were consulted about the creation of Adam, and they disputed it and said: Do not place a khaleefah (vicegerent) on earth."
Al-Sa’adi said: "‘… The chiefs on high when they were disputing and discussing’ means: ‘… when your Lord said to the angels: "Verily, I am going to place (mankind) generations after generations on earth"…’ [2:30]
Qutadah said: "The words ‘I had no knowledge of the chiefs on high when they were disputing and discussing’ refer to the angels, who disputed the creation of Adam when Allah said to them, (interpretation of the meaning) ‘Truly, I am going to create man from clay’.” [38:71].
As regards what was reported in the sunnah, Ibn ‘Abbas (may Allah be pleased with him and his father) narrated that the Messenger of Allah (peace and blessings of Allah be upon him) said that Allah spoke to him in a dream and said, "O Muhammad, do you know what the chiefs on high are disputing about?… about the things which expiate for sins. Things that expiate for sins are: staying in the mosque after the prayers, walking to join congregational prayers and performing wudu properly when it is difficult to do so. Whoever does these things will have a good life and die a good death, and he will be as free from sin as on the day his mother bore him." [Al-Tirmidhi])
In his commentary on this hadeeth (narration), al-Mubarakpuri explained that "the chiefs on high" (al-mala al-a’ala) referred to the angels who are closest to Allah. Al-mala refers to nobles who attend gatherings and sit at their head because of their high status. They are described as al-a’ala either because they live on high, or because of their high status in the sight of Allah. Their "dispute" refers either to their competing or rushing to record these deeds and take them up to heaven, or to their discussing the virtue and blessing of these deeds, or to their feeling happy about people when they do these good deeds. It may have been called a "dispute" because it came in the form of questions and answers, which sounds like a dispute or a debate, hence it was appropriate to use the word "dispute" in this context.
And Allah knows best.