Euler was a non-confrontational and deeply religious person. He was kind and could get on well with anyone. He worked under any circumstances and in any environment: “A baby on his lap, a cat on his back — that’s how he wrote his immortal works,” as one of his contemporaries said.
Usually this phrase is attributed to Dieudonné Thiébault, but we were unable to identify the source. However we found similar phrasing in Camille Paganel's Histoire de Frédéric le Grand, 1847, volume 1, page 448,
un chat sur l'épaule et ses enfant sur les genoux, rédigeait des mémoires admirés du monde savant.
Could you help me trace back the origin of this phrase (if this goes to Thiebault...)?