Is “Reining in the horse to remonstrate and gathering ferns on Shouyang Mountain, refusing to eat the grain of Zhou” true?
attested in history
The Records of the Grand Historian, in the biography of Bo Yi and Shu Qi, clearly records that they reined in King Wu's horse to remonstrate against his attack on the Shang ruler, and later, ashamed to eat the grain of Zhou, they hid on Shouyang Mountain, gathered ferns, and starved to death.
Bo Yi
In official history, he is the son of the孤竹 ruler at the end of the Shang dynasty, a noble hermit who refused to eat the grain of Zhou; in fiction, he is a symbol of unwavering loyalty to his lord.