In The Name of Allaah, The Most Merciful, The Bestower of Mercy.
Shaikhul Islaam Ibn Taymiyyah [rahimahullaah] said:
Groups amongst the people thought that the religion needed innovation, especially in their chosen path; but the affair is not as they thought, for indeed Allaah [The Exalted] said: [ٱلۡيَوۡمَ أَكۡمَلۡتُ لَكُمۡ دِينَكُمۡ وَأَتۡمَمۡتُ عَلَيۡكُمۡ نِعۡمَتِى وَرَضِيتُ لَكُمُ ٱلۡإِسۡلَـٰمَ دِينً۬اۚ – This day, I have perfected your religion for you, completed My Favour upon you, and have chosen for you Islam as your religion]. [Surah Al-Maa’idah. Aayah 3].
Likewise, other texts shows that the Messenger [sallal laahu alayhi wasallam] acquainted the Ummah with everything they need in their religious affairs. Allaah said: [وَمَا ڪَانَ ٱللَّهُ لِيُضِلَّ قَوۡمَۢا بَعۡدَ إِذۡ هَدَٮٰهُمۡ حَتَّىٰ يُبَيِّنَ لَهُم مَّا يَتَّقُونَۚ – And Allah will never lead a people astray after He has guided them until He makes clear to them as to what they should avoid]. [Surah At-Tawbah. Aayah 115]
The Messenger [sallal laahu alayhi wasallam] said: “Verily the one – among you – who lives long will see a lot of differing, so you must adhere to my Sunnah and to the Sunnah of the Khulafaa Ar Raashideen [the rightly guided caliphs], hold onto it firmly with your molar teeth” [i.e. adhere to it firmly].
Had it been that the Sunnah of the Prophet [sallal-laahu-alayhi wasallam] and that of the Khulafaa Ar-Raashideen is not suitable and sufficient for the believer during times of much differing, it would not be permissible to command that one [returns and adheres to it]. And also he [sallal laahu alayhi wasallam] used to say in his sermons, “The worst of all affairs [in the religion] are the newly invented matters and every innovation [in the religion] is misguidance”. [An Excerpt from Al-Istiqaamah. Pages 35-36. slightly paraphrased]