Allah the Almighty says in surah al-Nisa’, verse forty-nine:
‘Surely, Allah will not forgive that any partner be associated with Him; but He will forgive whatever is short of that to whomsoever He pleases. And whoso associates partners with Allah has indeed devised a very great sin.’
The Promised Messiah(as) says in this respect that:
Similarly, Allah has said in the Holy Qur’an:
This means that every sin is forgivable except shirk. Therefore, do not go near shirk and consider it to be a forbidden tree. (Damimah Tohfah-e-Golarhviyyah, Ruhani Khaza’in, vol. 17, pp. 323–324, footnote)
Then the Promised Messiah(as) says:
Shirk here does not merely mean bowing before stones, etc.; rather, it is also shirk that you should depend entirely on worldly means and emphasise worldly idols. This is what shirk is. (Al-Hakam, vol. 7, No. 24, June 30, 1903, p. 11)
Almighty Allah says in the Holy Qur’an:1
And remember when Luqman said to his son while exhorting him, ‘O my dear son! associate not partners with Allah. Surely, associating partners with God is a grievous wrong.’
The Holy Prophet(sa) feared the spread of shirk in his ummah [followers]. One hadith states:
‘Ubadah Bin Nasi told us about Shaddad Bin ’Aus that he was crying. He was asked, ‘Why do you cry?’ He replied, ‘I have remembered something that I heard from the Holy Prophet(sa) and it has made me cry. I heard the Holy Prophet(sa) say that, “I fear about shirk and their secret desires in my ummah.” I asked, “O Prophet of Allah, will your people be involved in shirk after you?” The Holy Prophet(sa) responded, “Yes, even though my people will not worship the sun and the moon, the idol and the stone, they will suffer from ostentations in their actions and they will be prey to their hidden desires. One of them will start the day fasting but then he will come across a desire and he will break the fast and indulge in his desire.”’ (Musnadu Ahmadabni Hanbal, vol. 4. p. 124, printed in Beirut)
1 Luqman, 31:14