It is known that those who defend innovations to gain mainstream acceptance, when discussing the topic of bid'ah (innovation) defines it as being both good and bad. What they do not reveal though is that these scholars (whom they quote) are simply using the word "bid'ah" in its broader linguistic sense, and not strictly in its Shari'ah sense.
Statements of some of the scholars such as al-Shafi'i, al-Izz bin Abd al-Salam, an-Nawawi and Ibn Hajar al-Asqalani are often cited to show agreement and acceptance, when in fact these deceptive short quotes reveal differently when we see the entire section.
Ibn Hajar al-Asqalani's Explanation
Ibn Hajar said in Fath al-Bari (13/278) in the book Holding Fast to the Book and Sunnah, in the chapter "What is disliked of delving and disputing in knowledge, exaggeration in the religion and innovations," the following:
وأما " البدع " فهو جمع بدعة وهي كل شيء ليس له مثال تقدم فيشمل لغة ما يحمد ويذم ، ويختص في عرف أهل الشرع بما يذم وإن وردت في المحمود فعلى معناها اللغوي
As for innovations (البدع), it is the plural of innovation (بدعة) and it is everything which does not have any prior example. Linguistically, [the word] encompasses what is both praiseworthy and blameworthy. In the usage of the people of the legislation (i.e. Scholars) it is specifically for what is blameworthy and if it is used in connection to what is praiseworthy, then it is upon its linguistic meaning.
And Ibn Hajar also said (13/253):
و " المحدثات " بفتح الدال جمع محدثة والمراد بها ما أحدث ، وليس له أصل في الشرع ويسمى في عرف الشرع " بدعة " وما كان له أصل يدل عليه الشرع فليس ببدعة ، فالبدعة في عرف الشرع مذمومة بخلاف اللغة فإن كل شيء أحدث على غير مثال يسمى بدعة سواء كان محمودا أو مذموما ،
And "the newly invented matters" (المحدثات), with the fathah on the daal, is the plural of novelty (محدثة) and what is intended by it is what has been newly-introduced and does not have any basis in the legislation. It is referred to in the usage of the Shari'ah as innovation (بدعة). As for what has a basis indicated by the Shari'ah then it is not an innovation. For "innovation" in the usage of the Shari'ah is blameworthy as opposed to its usage (with its) linguistic (meaning), for everything that has been newly-invented without any prior example is named "bid'ah" irrespective of whether it is praiseworthy, or blameworthy.
Ibn Kathir's Explanation
In support of the above, we find Ibn Kathir said in explanation of the verse (2:117):
والبدعة على قسمين تارة تكون بدعة شرعية كقوله فإن كل محدثة بدعة وكل بدعة ضلالة وتارة تكون بدعة لغوية كقول أمير المؤمنين عمر بن الخطاب عن جمعه إياهم على صلاة التراويح واستمرارهم نعمت البدعة هذه
And bid'ah is of two types. Sometimes it is a bid'ah shar'iyyah (with its Shariah meaning), such as his saying, "For every newly-invented matter is an innovation and every innovation is misguidance..." and sometimes it is a bid'ah lughawiyyah (with its linguistic meaning), such as the saying of Amir al-Mu'minin Umar bin al-Khattaab regarding his uniting them together for the Tarawih prayer and making them maintain this practice, "What an excellent innovation this is..."
The two statements from Ibn Hajar al-Asqalani and one from Ibn Kathir allow us to develop a context by which we can understand the true and real intent of those who have spoken of "good bid'ah". It is this context that those who are dishonest wish to conceal to justify their multitude of relative innovations (bid'ah idafiyyah) which are censured in the Shariah and which they try to justify by confusing them with matters which have been entered into the linguistic application of this term by a number of scholars.
Adapted from: "Refuting the Notion of Bid'ah Hasanah (Good Innovation) in Worship: Part 1" at bidah.com