The erroneous crucial conclusion, known as "the relativity of simultaneity", made in §2 of the founding 1905 paper can be found on page 897 of the German original:

In English it reads:

"Observers moving with the moving rod would thus find that the two clocks were not synchronous, while observers in the stationary system would declare the clocks to be synchronous."

or stated generally:

"So we see that we cannot attach any absolute signification to the concept of simultaneity, but that two events which, viewed from a system of co-ordinates, are simultaneous, can no longer be looked upon as simultaneous events when envisaged from a system which is in motion relatively to that system."