Salman on Khilafah: Unjust leaders are kings, not Caliphs

Salman al-Farisi reported: Umar Ibn al-Khattab, may Allah be pleased with him, said to him, “Am I a king or a Caliph?” Salman said, “Verily, if you take a single coin from the land of the Muslims, more or less, and place it where it does not belong, you are a king and not a Caliph.” When Umar heard this, he wept.

Source: al-Ṭabaqāt al-Kubrá 3787

عَنْ سَلْمَانَ أَنَّ عُمَرَ رضي الله عنه قَالَ لَهُ أَمَلِكٌ أَنَا أَمْ خَلِيفَةٌ فَقَالَ لَهُ سَلْمَانُ إِنْ أَنْتَ جَبَيْتَ مِنْ أَرْضِ الْمُسْلِمِينَ دِرْهَمًا أَوْ أَقَلَّ أَوْ أَكْثَرَ ثُمَّ وَضَعْتَهُ فِي غَيْرِ حَقِّهِ فَأَنْتَ مَلِكٌ غَيْرُ خَلِيفَةٍ فَاسْتَعْبَرَ عُمَرُ

3787 الطبقات الكبرى لابن سعد