Israel didn't give atomic weapons to South Africa. Israel and South Africa collaborated on their nuclear programs to a degree because they were both pariah states (Israel because of Palestine, South Africa because of apartheid) and had limited access to resources because of international embargoes. South Africa in particular had access to extensive uranium ore supplies (it was one of the top producers of it in the world), which Israel did not. Israel had a far more developed scientific and technical base than South Africa did. So there was definitely room for possible exchange and overlap.

As part of agreements started in 1976, the Israelis gave the South Africans some information about the practical manufacture of nuclear weapons, as well as some 30 g of tritium. In exchange the South Africans gave the Israelis yellowcake (processed natural uranium oxide). They also had agreements for exchanging information on conventional weapons (some of which were nuclear capable), and other arms agreements. The South African officials have repeatedly said that they didn't receive weapons design information, much less actual weapons, from any other country.

And of course, there is speculation that if the Vela incident was a nuclear test by Israel, that South Africa may have provided logistical support in exchange for test data. Whether that is true is pretty unclear.

That's a form of mutual assistance, but it is not a case of Israel "giving" South Africa the bomb in any meaningful sense. The South Africans did, in 1975 or so, contemplate whether Israel might sell them warheads, and probe the Israelis a bit on this, but this doesn't seem to have been pursued.

You can get a lot more details in David Albright's Revisiting South Africa's Nuclear Weapons Program: Its History, Dismantlement, and Lessons for Today (2016).