The primary text you are looking for is Vocal Wisdom: Maxims of Giovanni Battista Lamperti

Giovanni Battista Lamperti was born in 1839 in Naples, Italy, a city steeped in musical tradition. From a young age, Lamperti demonstrated a prodigious talent for singing, and he began his vocal studies at the Naples Conservatory. After completing his studies, Lamperti went on to enjoy a successful career as an opera singer, performing on the stages of Europe's leading opera houses.

"Do not 'sing'—listen to your tone." "The thought creates the act."