I have found the quote in A Feast for Crows:
"I wrote you letters," he said, "but Maester Joseran would not send them. Once I gave a stag to an oarsman on a trader bound for Lordsport, who promised to put my letter in your hands."
"Your oarsman winkled you and threw your letter in the sea."
"I feared as much. They never gave me your letters either."
I wrote none. In truth, she had been relieved when Tris was sent away.
Here's a new one:
"Pray for me if you like, I've forgotten all the words."