In part of a collection of the fataawa of Imam ‘Abd al-Rahman ibn Naasir al-Sa’di, he discusses the issue of al-bid’ah (innovation) as follows:

مسألة الخامسة العشرة في قول الجامع في البدعة

Issue number Fifteen – A Comprehensive Statement regarding Bid’ah

البدعة : هي الابتداع في الدين ، فإن الدين : هو ما جاء به النبي ﷺ في الكتاب والسنة ، ودلت عليه أدلة الكتاب والسنة ، فهو من الدين ، وما خالف ذلك ، فهو البدعة . هذا هو الضابط الجامع . وتنقسم البدعة بحسب حالها إلى قسمين : بدع إعتقاد ويقال لها : البدع القولية وميزانها قوله ﷺ في الحديث الذي في السنن ( وستفترق هذه الامة على ثلاثة وسبعين فرقة كلها في النار إلا واحدة ، قالوا : من هي يا رسول الله؟ قال: من كان على مثل ما أنا عليه اليوم وأصحابي ) فأهل السنة المحضة السالمون من البدعة الذين تمسكوا بما كان عليه النبي ﷺ وأصحابه في أصول كلها ، أصول التوحيد والرسالة والقدر ، ومسائل الإيمان وغيرها . ـ

al-Bid’ah: it is introducing something new into the deen. For indeed the deen is that which the Prophet (ﷺ) brought in the Book and the Sunnah, and what the evidences of the Book and the Sunnah indicate. So that is from the deen, and whatever opposes that, then that is bid’ah. That is the overarching principle. And bid’ah is divided according to its condition into two categories: 1) innovations of creed, and this is (also) referred to as al-bida’ al-qawliyyah (innovations of speech), and the standard against which this is measured is his (ﷺ) statement:

“This nation will divide into seventy-three sects, all of them in the Hell-fire except one” They said, “Who are they, O Messenger of Allah?” He said, “Those who are upon the likes of what I and my companions are on today.”

So the People of the pure Sunnah who are safe from al-bid’ah are those who cling to what the Prophet (ﷺ) and his companions were upon in regards to all the fundamental matters; the fundamentals of al-Tawheed and messengership and al-Qadr, and the issues of al-eemaan and other than that.

وغيرهم من خوارج معتزلة وجهمية وقدرية وروافضة ومرجئة ومن تفرع عنهم ، كلهم من أهل البدع الاعتقادية ، وأحكامهم متفاوتة بحسب بعدهم عن أصول الدين وقربهم ، وبحسب عقائدهم أو تأويلهم ، وبحسب سلامة أهل السنة من شرهم في الأقوال والأفعال وعدمه . وتفصيل هذه الجملة يطول جدا . ـ

And other than them [i.e. other than the People of the Sunnah] from the Khawaarij, the Mu’talizah, the Qadariyyah, the Rawaafidhah, the Murji’ah and those who have branched off from them – all of them are from the people of creedal innovations, and their respective rulings varying according to their distance or closeness to the fundamentals of the deen, and according to their creedal beliefs or false interpretations, and according to the safety – of lack thereof – of the People of the Sunnah from their harm – whether verbal of physical. And to elaborate all of that in detail would take a very long time.

والنوع الثاني : بدع عملية ، وهو أن يشرع في الدين عبادة لم يشرعها الله ولا رسوله ، وكل عبادة لم يأمر بها الشارع أمر إيجاب أو استحباب فإنها من البدع العملية ، وهي داخلة في قوله ﷺ : ( ومن عمل عملا ليس عليه أمرنا فهو رد ) ، ولهذا كان من أصول الأئمة الإمام أحمد وغيره : أن الأصل في العبادات الحضر المنع ، فلا يشرع منها إلا ما شرع الله ورسوله ، والأصل في المعاملات والعادات الإباحة ، فلا يحرم منها إلا ما حرم الله ورسوله ، ولهذا من قصور العلم جعل بعض العادات التي ليست عبادات بدعا لا تجوز ، مع أن الأمر بالعكس ، فإن الذي يحكم بالمنع منها وتحريمها هو المبتدع ، فلا يحرم من العادات إلا ما حرمه الله ورسوله ، بل العادات تنقسم إلى أقسام ، ما أعان منها على الخير والطاعة ، فهو من القرب . وما أعان على الإثم والعدوان ، فهو من المحرمات ، وليس فيه هذا ولا هذا ، فهو من المباحات ، والله أعلم . ـ

And 2) the second category [of bid’ah] is bid’ah ‘amaliyyah (innovations of deed), and that is legislating in terms of the deen an act of worship which neither Allah nor His messenger legislated. And every act of worship which the Divine Legislator did not command us with an order of obligation or recommendation, then it among the innovations of deed, and this falls under his (ﷺ) statement:

Whoever does an action which is not from our way, then he will have it rejected.

And due to this, it is from the foundations of the imams – Imam Ahmad and other than him – that the fundamental principle regarding acts of worship is halting and prohibition, so nothing is legislated of them except for what Allah and His messenger legislated. And the fundamental principle regarding acts of human interaction and custom is permissibility, so nothing is prohibited of these except what Allah and His messenger have prohibited. So in line with this is that it is from limited knowledge to hold some of the acts of custom which are not acts of worship as innovations which you do not allow, since the situation is actually the reverse. For the one who makes a ruling of prohibition and impermissibility of that is himself an innovator, for nothing of the customary acts are prohibited except what Allah and His messenger have prohibited. Rather, the customary acts are divided into three categories; 1) those of them that aid in goodness and obedience, so these are from the things which bring about closeness (to Allah). And 2), those that aid in sin and enmity, so they are from the forbidden things. And 3), those which are neither from this category nor that category, so they are from the permissible things. And Allah knows best.