Where did Yan Zhenqing learn calligraphy?

When Yan Zhenqing was young, his family was poor and lacked paper and pens, so he used a pen to brush loess water to practice calligraphy on the wall. Chu Suiliang, a beginner, studied under Zhang Xu and learned from the characteristics of the four schools in the early Tang Dynasty. Zhuan Xu and Yan Zhenqing from the Northern Wei Dynasty were also collected. When they were young, their paper and pens were poor, and they practiced calligraphy on the wall with pens. Chu Suiliang, a beginner, studied under Zhang Xu and four masters in the early Tang Dynasty. He not only accepted the seal script, but also accepted the writing style of the Northern Wei Dynasty, which made him unique. Contrary to the writing style of the early Tang Dynasty, he changed from thin and hard to full and vigorous, with great momentum. He is called "Yan Ti". Yan Ti has established his immortal status of regular script for thousands of years, and Yan Zhenqing is one of the influential calligraphy masters in the history of China calligraphy. His "Yan Ti", together with Liu Gongquan, is also called "Yan Liu" and has the reputation of "Yan Liu Jin Gu". The style of writing is unique, which is contrary to the calligraphy style of the early Tang Dynasty. It turns thinness and hardness into fullness and vigor, and has a broad and magnificent momentum. It's called "Yan Ti". Yan Ti has established his immortal status of regular script for thousands of years, and Yan Zhenqing is one of the influential calligraphy masters in the history of China calligraphy. His "Yan Ti", together with Liu Gongquan, is also called "Yan Liu" and has the reputation of "Yan Liu Jin Gu".