Belarus sold the s-300's to Iran. Israel payed Belarus to supply s-300's with hidden modifications that allows the IDF to take over control of the launchers and disrupt the missiles flightpass. Belarus makes some dosh on both side and Mahmoud gets screwed 'Iranian style' . All ends well.
Saudi king to meet with Obama on Friday amid Gulf concerns over Iran deal (Reuters)
from the article: Iran official: We have obtained the S-300 missile system