Rashi on Exodus 22:21/רש"י על שמות כ״ב:כ״א

1כל אלמנה ויתום לא תענון YOU SHALL NOT AFFLICT ANY WIDOW, OR FATHERLESS CHILD — That is also the law regarding any person, but Scripture is speaking of what usually happens and therefore mentions these in particular, for they are feeble in defensive power (i. e. they have no one to protect them) and it is a frequent occurrence for people to afflict them (Mekhilta).