If you'd asked we'd have told you that 4.2V or even 5V is not
enough head room to safely run a LED with 800ma @ 3.8V
and use a current limiting resistor.
You could do 5V with an active current limit.
We tell you that you are doing it wrong and your response,
despite the large number of others telling you it was wrong
and why, you insist it was OK because you, the battery
and the LED seemed to have survived.
We all make mistakes. Most try to learn from them.
It was your continued insistence that you did nothing wrong
that cause the progressive stronger replies.
It has been stated several times to you that the voltage stated
is just an approximate voltage, useful for estimating a current
limiter.
It is not to say that you can connect the same voltage to
is and expect proper operation.
The specification are not there as a learning tool for those
that don't have the slightest idea as to what they are doing.
They are there for an engineer that already knows that
LEDs require current limiting.
The voltage rating was there to assist in a proper designed
current limit.
Dwight