Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos)
By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
First Section – the Positive Commandments
69. It is a positive commandment to return a Jew's lost object
As it states in Devarim (Deuteronomy) 22:1, "You shall return, you shall surely return to your brother." If a person turns his eyes from it, he has transgressed a positive and a negative commandment (see Negative Commandment 182). If he picks up the lost object but does not return it, he has also violated this positive commandment and two negative commandments (Negative Commandments 35 and 182). Even if the lost object belongs to a wicked person, it is a commandment to return it to him. If the owner of the object eats unkosher meats to get others upset or transgresses Shabbos publicly, he is considered a heretic, and it is forbidden to return the lost object to him. If the object that is found is something that is not honorable for the person to pick up and if it was his own, he would not bother to pick it up, he is not required to pick it up. If he wants to go beyond the letter of the law in this matter, he may, and a blessing will come to him.
Rabenu Yona writes: if it is a commandment to care for a person's property, how much more so is it a commandment to care for a person's wellbeing and help him during a time of sadness.
This applies in all places and at all times, for men and for women.