There is a title "Knotting Socks" in the lyrics of Zaqu. Can anyone tell me its origin?

In the past, people's socks were very thick and high, and they fell off easily, so they had to be tied around their legs with straps (in the past, people with status had to wear socks on important occasions. If the socks fell off and they It is rude to ignore someone). When Zhang Shizhi was a Taiwei, an old man named Wang Sheng was summoned by the emperor. Wang Sheng deliberately untied the laces of his socks, and then said to Zhang Shizhi: "My garters are untied, please tie them for me." Come on!" Zhang Shizhi tied Wang Sheng's garter in the palace in front of all the civil and military officials. After leaving the court, the ministers complained about Wang Sheng, saying how could you humiliate Captain Zhang like this? Wang Sheng replied: "I am old, and I may not be able to help Zhang Taiwei until I die, so I do this to let others know how Taiwei respects the elderly and the virtuous, so that people in the world can Everyone respects him!" Everyone respects Zhang Shizhi even more. Later, "knotting socks" was used as a metaphor to repay kindness and sacrifice one's life. Wen Zisheng in the later Wei Dynasty and Li Bai in the Tang Dynasty both wrote poems with this theme.