וַיִּרְא֣וּ אֶחָ֗יו כִּֽי־אֹת֞וֹ אָהַ֤ב אֲבִיהֶם֙ מִכָּל־אֶחָ֔יו וַֽיִּשְׂנְא֖וּ אֹת֑וֹ וְלֹ֥א יָכְל֖וּ דַּבְּר֥וֹ לְשָׁלֹֽם׃
And when his brethren saw that their father loved him more than all his brethren, they hated him, and could not speak peaceably unto him.
Rashi on Genesis
ולא יכלו דברו לשלום AND THEY COULD NOT SPEAK PEACEABLY TO HIM — from what is stated to their discredit we may infer something to their credit: they did not speak one thing with their mouth having another thing quite different in their hearts (Genesis Rabbah 84:9).
Sforno on Genesis
ויראו אחיו כי אותו אהב אביהם, here Yaakov had committed an error, allowing the love in his heart for Joseph to be now become visible through preferential treatment of him.
Radak on Genesis
ולא יכלו דברו לשלום, any conversation with Joseph did not revolve around peacefully discussed matters of common interest, but concerned only matters of dispute between them.