An ayah

What happened between Musa and Harun after Musa returned
Allah informs of what happened when Musa returned to his people and saw the great matter that had taken place among them. With this he became filled with anger and he threw down the Divine Tablets that he had in his hand. Then, he grabbed his brother Harun by his head and pulled him towards himself. We expounded upon this previously in Surat Al-A`raf, where we mentioned the Hadith,
«لَيْسَ الْخَبَرُ كَالْمُعَايَنَة»
(Information is not the same as observation.) Then, he began to blame his brother, Harun, by saying,
[مَا مَنَعَكَ إِذْ رَأَيْتَهُمْ ضَلُّواْأَلاَّ تَتَّبِعَنِ]
(What prevented you when you saw them going astray; that you followed me not) meaning, "You should have informed me of this matter as soon as it happened.''
[أَفَعَصَيْتَ أَمْرِى]
(Have you then disobeyed my order) "In that which I entrusted to you,'' referring to Musa's statement,
[اخْلُفْنِى فِى قَوْمِى وَأَصْلِحْ وَلاَ تَتَّبِعْ سَبِيلَ الْمُفْسِدِينَ]
(Replace me among my people, act in the right way and follow not the way of the mischief-makers.)[7:142]
[قَالَ يَبْنَؤُمَّ]
(He (Harun) said: "O son of my mother!'') This mentioning of the mother was Harun's attempt to soften Musa's anger, because he was Musa's biological brother and they had the same parents. The mentioning of the mother here is more delicate and profound in bringing about gentleness and mildness. This is why he said,
[يَبْنَؤُمَّ لاَ تَأْخُذْ بِلِحْيَتِى وَلاَ بِرَأْسِى]
(O son of my mother! Seize (me) not by my beard, nor by my head!) This was Harun's excuse to Musa for being delayed from coming to him and informing him of the great mishap that took place. He said,
[إِنِّى خَشِيتُ]
(Verily, I feared) meaning, "I was afraid to come after you and inform you of this, because I thought you might accuse me of leaving them alone and causing division between them.''
[وَلَمْ تَرْقُبْ قَوْلِى]
(and you have not respected my word!) This means, "And you did not take care of what I commanded you to do when I left you in charge of them.'' Ibn `Abbas said, "Harun was respectful and obedient to Musa.''




http://tafsir.com/default.asp?sid=20&tid=32352

asalam alykum

Prophet Musa went to talk to Allah at the mountain. And some people started to make a cow made of gold to worship (because they were influenced by idol worshippers.)

So the above happened.

read from verse 83 onwards and you will get it.