Shirk is greatest injustice

Luqman 31:13

وَاِذۡ قَالَ لُقۡمٰنُ لِابۡنِہٖ وَہُوَ یَعِظُہٗ یٰبُنَیَّ لَا تُشۡرِکۡ بِاللّٰہِ ؕؔ اِنَّ الشِّرۡکَ لَظُلۡمٌ عَظِیۡمٌ

And [mention, O Muhammad], when Luqman said to his son while he was instructing him, "O my son, do not associate [anything] with Allah. Indeed, association [with Him] is great injustice."

Al-Ma'idah 5:72

لَقَدۡ کَفَرَ الَّذِیۡنَ قَالُوۡۤا اِنَّ اللّٰہَ ہُوَ الۡمَسِیۡحُ ابۡنُ مَرۡیَمَ ؕ وَقَالَ الۡمَسِیۡحُ یٰبَنِیۡۤ اِسۡرَآءِیۡلَ اعۡبُدُوا اللّٰہَ رَبِّیۡ وَرَبَّکُمۡ ؕ اِنَّہٗ مَنۡ یُّشۡرِکۡ بِاللّٰہِ فَقَدۡ حَرَّمَ اللّٰہُ عَلَیۡہِ الۡجَنَّۃَ وَمَاۡوٰىہُ النَّارُ ؕ وَمَا لِلظّٰلِمِیۡنَ مِنۡ اَنۡصَارٍ

They have certainly disbelieved who say, "Allah is the Messiah, the son of Mary" while the Messiah has said, "O Children of Israel, worship Allah, my Lord and your Lord." Indeed, he who associates others with Allah – Allah has forbidden him Paradise, and his refuge is the Fire. And there are not for the wrongdoers any helpers.