Now Moses selected from his people seventy men (to take with him) to Our appointed place and time, but when the earthquake seized them he said, ‘My Lord! if You so willed You could have destroyed them as well as me before (this). But would You destroy us on account of that which the foolish among us have done? This (matter of the calf) is nothing but (an ordeal from You) that You may distinguish the good from the bad (of us). You adjudge, by such means, to be astray whomsoever You will and You guide whomsoever You will. You are our Patron, protect us therefore, and have mercy on us, for You are the Best of Protectors (against the consequence of our faults). (7:155) 
Commentary
NUMBER 70: There are many recollections in the Quran about Prophet Mūsā and the interaction with his companions; at times they were devoted to him and Allah and listened to what he ordered them to do; at other times, as in this verse, we are given a glimpse of their strange behavior with this great prophet – one who saved the Banī Isrāʾīl from the grips of the Pharaoh.
Prophet Mūsā was set to “meet” Allah and on this special gathering, he chose, as this verse of the Quran clearly tells us, 70 people from amongst Banī Isrāʾīl – why 70 and not more or less – that is not known to the commentators of the Quran, however this number must have some significance to it. 
Since his companions were not able to hear the words of Allah, something which Mūsā was obviously able to do, they requested or rather demanded that Allah SHOW Himself to them “in the flesh”. 
Such a thing is impossible and so, although in this portion, Allah does not go into the details of what happened as He has done in other chapters, but we are told that a ‘temporary retribution’ took over Mūsā and his community which knocked everyone unconscious. 
Prophet Mūsā appealed to His Creator asking Allah not to make the good people of the community face a humiliating defeat due to the foolish, irrational (أَلسُّفَهَاءُ مِنَّا) people from amongst them.
It was not only this one thing which the Children of Isrāʾīl were guilty of – they had been saved from bondage and were given countless blessings by Allah including Him sending down a wide variety of food, however they resorted to idol worship and many other sins and then to top it off, they asked to “see” Allah! 
Nonetheless, Prophet Mūsā prayed to Allah to forgive everyone and to have mercy upon him and his community and sincerely asked for the guidance of his nation.
Point of Reflection
In the world today,  there are many people who call themselves “Muslims”, however they are far from being a representation of the true faith. We must always ensure our non-Muslim acquaintances and the media do not label us as being the same and do not hold us to account because of the ‘foolish ones’ from amongst us.