Praise be to Allah.the Lord of the Worlds, and peace and blessings be upon his truthful Prophet.
Firstly, how can there be any such thing as bidah hasanah (good innovation) when the Prophet (peace and blessings of Allaah be upon him) said: Every bidah is a going astray and every going astray is in Hell-fire. So, if anyone says that there is such a thing as bidah hasanah, he can only be insisting on going against the Messenger of Allaah (peace and blessings of Allaah be upon him).
Secondly, saying al-hamdu Lillaah (praise be to Allaah) when coming out of rukoo is a well-known phrase of dhikr which is proven in sound ahaadeeth reported from the Prophet (peace and blessings of Allaah be upon him). All that this Sahaabi did was to come up with a new phrase expressing praise to Allaah. How can this be used as evidence to support innovations in worship and dhikr that have no basis in the sources of Islam?
Thirdly, what this Sahaabi did cannot be taken as evidence in and of itself. It was not even considered to have been a correct action until after the Prophet (peace and blessings of Allaah be upon him) had approved it, and not before. But how on earth could this innovator obtain the approval of the Prophet (peace and blessings of Allaah be upon him) after he has passed away?"
Fourthly, if we accept the use of this report as evidence, it is still no more than an isolated incident which cannot be generalized, whereas the hadeeth every bidah is a going astray is clearly a general statement. It is a well-known principle among the ulamaa (scholars) that what is stated clearly takes precedence over what is merely implied.
Fifthly, how can we know what is good or not with our limited minds alone and without the input of Revelation? Is there not the possibility of differences of opinion? What one person sees as good will be seen differently by another, so what would the standard be? Whose reasoning could we rely on or refer to? Would this not be confusion, even anarchy itself?
Sixthly (which confirms the third point made above), when the Prophet (peace and blessings of Allaah be upon him) approved of an act of worship or a dhikr (remembrance of Allaah) on the part of one of his Sahaabah, it would thus become a part of shareeah and hence be regarded as a sunnah hasanah. But with the death of the Prophet (peace and blessings of Allaah be upon him) and the ceasing of Revelation, how can we know whether innovated acts of worship or dhikr are correct or would be approved? We have no way of knowing, so we should limit ourselves only to the forms of worship that have been narrated in sound reports.
The great scholar al-Haafiz ibn Hijr (may Allaah have mercy on him) narrated many comments by Shaykh al-Islam Ibn Taymiyah in Fath al-Baari; he agreed with some and disagreed with others. This is the business of the scholars: they discuss and debate with one another, with the aim of reaching the truth which may lie with the one who is disagreeing or with the one whose opinion is being criticized. As for the unpleasant comment quoted in the question, from what we know of Ibn Hijr (may Allaah have mercy on him) and his good manners, fear of Allaah, awareness of the value of knowledge and respect for the scholars, we are sure that this comment is a fabrication. May Allaah forgive all the scholars and reward them for their efforts and concern.