2. " and give the orphans their property, and do not exchange something bad
(of yours) for something good (of theirs), nor devour their
property along with your own; (for) it is surely a great crime."

occasion of revelation:
 at the time of the prophet of islam (p.b.u.h.), one of the members of
a tribe by the name of bani-q­atfan had a rich brother, and it happened
that the rich brother passed away. then, as a guardian of his brother's
orphans, he took his property in his possession, but when his brother's son
matured and demanded it, he denied returning his right to him. the
subject was explained to the holy prophet (p.b.u.h.). then this verse was
revealed, and when the man heard it, he repented and returned the
property to its owner. then the man said: " i refuge with allah from that i
be polluted through the great sin."

commentary:
 treachery in orphans' property is forbidden!

in any society it happens that, as a result of some events and
accidents, some parents die and there remain some little children from
them.

there are three important instructions upon the property of orphans
mentioned in this verse.

1. at first, it instructs as such:

" and give the orphans their property, ..."

this ordinance means that your interference in these properties is in
the rank of a trustee and as an inspector, not as a possessor.

2. the second instruction is to prevent guardians from devouring the
property of orphans.

sometimes it happens that some guardians of the orphans, under the
pretext that changing the property of the orphan is benefitable for the
orphan, or it makes no difference to change it, or if it remains it will be
wasted, take the best and choice parts of the properties of the orphans and
put their own bad and undemanded properties in their places. the qur'an
says:

"... and do not exchange something bad (of yours) for something good
(of theirs),..."

3. the third instruction has been added as follows:

"... nor devour their property along with your own; ..."

this sentence means that: do not mix the property of the orphans
with your own property so that its result ends to the possession of the
whole. or, do not mix your undesirable property with their good property
so that its result be treading the rights of the orphans.

at the end of the verse, to emphasize and prove the importance of
the matter, ö that this kind of transgression to the property of the orphans
is a great sin, it says:

"... (for) it is surely a great crime."