Is the saying, "A man's praise of his brother kills him," an authentic Hadith, and what is the ruling on praising others, and how can one express gratitude and appreciation to a teacher?

The student's praise for their teacher is permissible if it is an acknowledgment of kindness, appreciation, and respect, provided that it does not involve lies or exaggeration. It is preferable to say: "I reckon him to be so, and I do not purify anyone before Allah." The permissibility of praising one who does good is indicated by the Prophet's (peace be upon him) saying: "Whoever is shown kindness and finds no reward for it except praise has indeed thanked him," and "He who does not thank people does not thank Allah."