Schumann said the following on a performance by Chopin of his Etude in A flat major Op. 25 no. 1:
"It would be a mistake to suppose that he made all the small notes individually audible: it was more an undulation of the A flat major chord, lifted here and there high up on the keyboard, with the help of the pedal. But, exquisitely entangled in the harmony, one perceived the wonderful, deep-toned melody, and just in the middle section did a tenor voice emerge clearly from the chords to join the principal melody. And when the etude was ended, we felt as though we had seen a radiant picture in a dream which, half awake, we ached to recover. Then he played the second etude in the book, in F minor."
Some quotes from Mikuli, one of Chopins pupils and an editor of the publication of several of his works:
"Under Chopins hands the piano needed to envy neither the violin for its bow nor wind instruments for their living breath. The tones melted into one another as wonderfully as the most beautiful singing. The tone which he could draw from the instrument, especially in cantabile, was immense; in this regard John Field alone could be compared with him."
" Chopin took particular pleasure in playing [...] Field's Nocturnes, to which he would improvise the most beautiful
fiorituras"
"He gave a noble, manly energy to appropriate passages with overpowering effect - energy without roughness - just as, on the other hand, he could captivate the listener through the delicacy of his soulful rendering - delicacy without affectation."
These quotes are from the "Chopin: pianist and teacher as seen by his pupils" by Eigeldinger. Highly recommended reading
Topic: How did Chopin play?