It is forbidden to say that an individual lacks commitment in fulfilling a particular commandment. Therefore, it is forbidden to say that a man set aside little time for daily Torah study, or that he does not go out of his way to help others.
This would apply even if the speaker and listener themselves study little (or are not known for their benevolence), and will openly admit to this without shame. Since the Torah command us to make Torah study and chesed performance priorities in our lives, it is forbidden to say that someone else lacks dedication in these areas.
Sefer Chofetz Chaim, 3 Tishrei, page 54