文天祥's poem 《过零丁洋》 ends 人生自古谁无死，留取丹心照汗青 'since ancient times, who has not died? Let me leave a loyal heart to shine in the annals'. He wrote it as a prisoner of the Mongols, who later executed him when he refused to serve them.
usage
丹 is cinnabar red, the color of sincerity. The set phrases are 一片丹心 'utter devotion' and 碧血丹心 'loyal to the death'.
