This excerpt is taken from Sheikh Ghulam Mustafa Zaheer Amanpuri's book Aamad Mustafa ﷺ.
Linguistic Innovation is Not Blameworthy
◈ Hafiz Ibn Hajar, may Allah have mercy on him (d. 852 AH), writes:
ليس له أصل فى الشرع، ويسمى فى عرف الشرع بدعة، وما كان له أصل يدل عليه الشرع، فليس ببدعة، فالبدعة فى عرف الشرع مذمومة بخلاف اللغة .
"Any act for which there is no basis in the Shariah is legally called an innovation (bid'ah). Any act for which there is a basis and evidence is not an innovation. Therefore, that which is called bid'ah in the Shariah is blameworthy; in the linguistic sense, bid'ah is not blameworthy."
Reference: (Fath al-Bari: 253/13)
◈ Hafiz Ibn Rajab, may Allah have mercy on him (d. 795 AH), writes:
كل بدعة ضلالة من جوامع الكلم، لا يخرج عنه شيء، وهو أصل عظيم من أصول الدين، وهو شبيه بقوله: من أحدث فى أمرنا ما ليس منه؛ فهو رد ، فكل من أحدث شيئا، ونسبه إلى الدين، ولم يكن له أصل من الدين يرجع إليه؛ فهو ضلالة، والدين بريء منه، وسواء فى ذلك مسائل الاعتقادات، أو الأعمال، أو الأقوال الظاهرة والباطنة، وأما ما وقع فى كلام السلف من استحسان بعض البدع، فإنما ذلك فى البدع اللغوية، لا الشرعية .
"The Prophet Muhammad, peace be upon him, said: Every innovation is misguidance. This statement is among the comprehensive sayings; no act is excluded from its ruling. This hadith is a great principle of the religion, and it is similar to the prophetic statement: Whoever introduces into our religion something for which there is no basis in it (the Book, Sunnah, and consensus), it is falsehood. Thus, if an act is attributed to the religion but its foundation is not based on any principle of the religion, that act will be called misguidance, and the religion is free from it. Whether it relates to matters of belief or outward and inward sayings and actions. In some statements of the pious predecessors, some innovations have been praised; this praise is for linguistic innovations, not for legal (Shariah) innovations."
Reference: (Jami' al-'Ulum wal-Hikam p. 193)
It is understood that every innovation is blameworthy, whether it relates to belief or actions; therefore, it is completely wrong to say:
"It has been established that bid'ah refers to belief."
Reference: (Ja'a al-Haqq p. 205)
Because the texts condemning innovations are general; no specification or division is established in them.
After the Era of the Companions, There Is No Good Innovation
◈ Allama Ibn Abi al-Izz Hanafi, may Allah have mercy on him (d. 792 AH), writes:
إن ما أحدث بعد عهد الصحابة لا يكون حسنا .
"No innovation that emerged after the era of the Companions can be a good innovation."
Reference: (At-Tanbih 'ala Mashakil al-Hidayah: 493/8)
It is established that the practice of the Companions is not an innovation; whoever has called it an innovation meant it in the linguistic sense, not the legal (Shari') sense.