Shaykh Muhammad ibn ‘Uthaymeen (may Allah have mercy on him) said:

“According to Sharee’ah, the definition is ‘Worshipping Allah in ways that Allah has not prescribed.’ If you wish, you may say, ‘Worshipping Allah in ways that are not those of the Prophet (peace and blessings of Allah be upon him) or his rightly guided successors (al-khulafaa’ al-raashidoon).’

The first definition is taken from the aayah (interpretation of the meaning):

“Or have they partners with Allah (false gods) who have instituted for them a religion which Allaah has not ordained?”

[42:21]

The second definition is taken from the hadeeth of the Prophet (peace and blessings of Allah be upon him), who said:

“I urge you to adhere to my way (Sunnah) and the way of the rightly-guided successors (al-khulafa’ al-raashidoon) who come after me. Hold fast to it and bite onto it with your molar teeth [i.e., cling firmly to it], and beware of newly-invented matters.”

So everyone who worships Allah in a manner that Allah has not prescribed or in a manner that is not in accordance with the way of the Prophet (peace and blessings of Allah be upon him) or his rightly-guided successors (al-khulafa’ al-raashidoon), is an innovator, whether that innovated worship has to do with the names and attributes of Allah, or to do with His rulings and laws.

With regard to ordinary matters of habit and custom, these are not called bid’ah (innovation) in Islam, even though they may be described as such in linguistic terms. But they are not innovations in the religious sense, and these are not the things that the Prophet (peace and blessings of Allah be upon him) was warning us against.

And there is no such thing in Islam as bid’ah hasanah (good innovation).”

From: Majmoo’ Fataawa Ibn ‘Uthaymeen, vol. 2, p. 291
4:50 AM

al-’Allaamah ‘Abdul-Azeez ibn Baaz (rahimahullaah) said:

…He should advise his brothers, however, with gentleness and kind speech, and not with transgression upon the people, nor harming them, insulting them, or cursing them. Rather with kind speech and a beautiful approach.

Allah (azza wa jall) said:

Invite to the way of your Lord and fair preaching, and argue with them in a way that is better

[16:125]

He, the Most High said;

And by the Mercy of Allah, you dealt with them gently

[3:159]

And Allah said to Moosa and Haaroon when He sent them to Fir’awn;

And speak to him mildly, perhaps he may accept admonition or fear (of Allah)

[40:44]

The Prophet (sallallaahu alayhi wa sallam) said;

“Indeed, gentleness is not to be found in anything but that it adds to its beauty, and it is not withdrawn from anything but it makes it defective”

[Saheeh Muslim hadeeth no. 2594, Sunan Abu Dawud hadeeth no. 4808, Musnad Ahmed 6/125)]

This is the case in this era. This era is the time of gentleness, patience and wisdom. It is not an era of harshness.

The majority of people are in ignorance, heedlessly indulging in the worldly life. Therefore, it is necessary to have patience and gentleness so the Da’wah can reach the people, until it has been conveyed to the people and until they have learned it.

We ask Allah guidance for everyone.

Source: Majmoo’ Fataawa 8/376