In The Name of Allaah, The Most Merciful, The Bestower of Mercy.

Allaah [The Exalted] said: [ يَـٰٓأَيُّهَا ٱلنَّاسُ كُلُواْ مِمَّا فِى ٱلۡأَرۡضِ حَلَـٰلاً۬ طَيِّبً۬ا وَلَا تَتَّبِعُواْ خُطُوَٲتِ ٱلشَّيۡطَـٰنِ‌ۚ إِنَّهُ ۥ لَكُمۡ عَدُوٌّ۬ مُّبِينٌ – O mankind! Eat of that which is lawful and good on the earth, and follow not the Khutuwaat of Shaitan (Satan). Verily, he is to you an open enemy]. [إِنَّمَا يَأۡمُرُكُم بِٱلسُّوٓءِ وَٱلۡفَحۡشَآءِ وَأَن تَقُولُواْ عَلَى ٱللَّهِ مَا لَا تَعۡلَمُونَ – he commands you only what is ‘Soo and Fahsha’, and that you should say against Allah what you know not]. [Surah Al-Baqarah. Aayaat 168-169]

[وَلَا تَتَّبِعُواْ خُطُوَٲتِ ٱلشَّيۡطَـٰنِ‌ۚ -and follow not the Khutuwaat of Shaitan (Satan)]. The meaning of shaytaan’s khutuwaat is his path and behaviour. [إِنَّهُ ۥ لَكُمۡ عَدُوٌّ۬ مُّبِينٌ – Verily, he is to you an open enemy]- Meaning, his enmity is manifest due to that which ocurred him and Adam.

[إِنَّمَا يَأۡمُرُكُم بِٱلسُّوٓءِ وَٱلۡفَحۡشَآءِ – he commands you only what is Soo and Fahsha] Meaning, every sin and ugly deed, and every sin that has a prescribe Sharee’ah punishment. [وَأَن تَقُولُواْ عَلَى ٱللَّهِ مَا لَا تَعۡلَمُونَ – and that you should say against Allah what you know not]- Meaning, shaytaan makes forbidden for them that which Allaah has not forbidden. [1]

Shaikhul Islaam Ibn Taymiyyah [may Allaah have mercy upon him] said: Indeed, there has been much confusion in this subject matter, just as it is the case in the subject matter of halaal and haraam. Indeed, a group of people make permissible some of the things which Allaah has declared impermissible and others declare impermissible some of those things which Allaah has made permissible. Likewise, some people innovate acts of worship that have not been legislated by Allaah; rather Allaah [The Most High] prohibited them. The foundation of the religion of Islaam is that the permissible affairs are those that Allaah and His Messenger have made permissible, and the impermissible affairs are those that Allaah and His Messenger have made impermissible. It is not allowed for anyone to leave the straight path which Allaah sent His Messenger with. Allaah [The Most High] said:

[وَأَنَّ هَـٰذَا صِرَٲطِى مُسۡتَقِيمً۬ا فَٱتَّبِعُوهُ‌ۖ وَلَا تَتَّبِعُواْ ٱلسُّبُلَ فَتَفَرَّقَ بِكُمۡ عَن سَبِيلِهِۦ‌ۚ ذَٲلِكُمۡ وَصَّٮٰكُم بِهِۦ لَعَلَّڪُمۡ تَتَّقُونَ – And verily, this is my Straight Path, so follow it, and follow not [other] paths, for they will separate you away from His Path. This He has ordained for you that you may become pious]. [Surah Al-An’aam. Aayah 153]

Abdullaah Ibn Mas’ood [may Allaah be pleased with him] reported that the Prophet [peace and blessings of Allaah be upon him] drew a line for us and said, “This is Allaah’s Straight Path”. He drew lines to its right and left and then said, “These are other paths, upon every one of them there is a devil calling towards it”. Then he recited:

[وَأَنَّ هَـٰذَا صِرَٲطِى مُسۡتَقِيمً۬ا فَٱتَّبِعُوهُ‌ۖ وَلَا تَتَّبِعُواْ ٱلسُّبُلَ فَتَفَرَّقَ بِكُمۡ عَن سَبِيلِهِۦ‌ – Indeed this is My Straight Path, so follow it. And do not follow other paths; they will separate you from His Path. [Al-Musnad 4437]

Indeed, Allaah mentioned – in Surah Al-An’aam, Surah Al-A’raaf and other them – those deeds which the idol worshipers were rebuked for, when they declared impermissible the things which Allaah [The Most High] did not declare impermissible, such as the Baahirah [a she-camel whose milk was spared for the idols and nobody was allowed to milk it] and the Saa’ibah [a she-camel let loose for free pasture for their false gods, e.g. idols, etc., and nothing was allowed to be carried on it]. They declared permissible those deeds which Allaah declared impermissible, such as the killing of their children and they instituted a religion which Allaah did not allow. Allaah [The Most High] said: [أَمۡ لَهُمۡ شُرَڪَـٰٓؤُاْ شَرَعُواْ لَهُم مِّنَ ٱلدِّينِ مَا لَمۡ يَأۡذَنۢ بِهِ ٱللَّهُ‌ۚ – Or have they partners with Allah (false gods), who have instituted for them a religion which Allah has not allowed] [Surah Ash-Shurah. Aayah 21]

And there were impermissible deeds which they established as acts of worship, such as polytheism and lewd behaviour, such as Tawaaf around the Kabah whilst being naked. [2]

[Ref 1: An Excerpt from ‘Zaadul Maseer Fee Ilmit Tafseer’. Slightly paraphrased]
[Ref 2: An Excerpt from ‘Al-Ibaadaat Ash-Shar-iyyah Wal-Farqu Baynahaa Wa Baynal Bid’ah page: 7-9. Slightly paraphrased]