Ayub added 65 runs for the second wicket with Babar Azam (27) after Nandre Burger dismissed opener Fakhar Zaman for nought with the second ball of the innings.
Azam fell run out, much to the disappointment of a packed 16,000 Iqbal Stadium in Faisalabad, having now gone 32 innings without an ODI hundred.
Ayub fell to spinner Bjorn Fortuin before Mohammad Rizwan, 32 not out, and Salman Agha, five not out, completed the chase.
The ODI series win is Pakistan's first against South Africa at home, having lost 3-2 twice in 2003 and 2007.
Pakistan won the first match by two wickets and South Africa took the second by eight wickets, also in Faisalabad.
Victorious skipper Shaheen Shah Afridi said: "It's a complete team effort and a reward for hard work."
Pakistan's captain Shaheen Shah Afridi holds the trophy during a ceremony at the end of the third and final one-day international (ODI) cricket match against South Africa at the Iqbal Stadium in Faisalabad on November 8, 2025. (Photo by AAMIR QURESHI/AFP via Getty Images)
Shaheen, captaining Pakistan for the first time in ODIs, added: "This win will give us confidence for the coming matches."
Visiting skipper Matthew Breetzke praised Abrar.
"We wanted a total of 250-plus but Abrar bowled very well and we lost too many wickets," said Breetzke, standing in for injured skipper Temba Bavuma.
Earlier, Abrar combined with Salman Agha (2-18) and pacer Shaheen (2-18) routed South Africa who won the toss and batted, but only four batters crossed double figures.
Quinton de Kock followed his hundred in the second match with a top score of 53 off 70 balls with a six and six boundaries while Lhuan-dre Pretorius knocked a 45-ball 39 with a six and four boundaries.
When on 44, De Kock completed 7,000 runs in 158th innings, the second fastest to the milestone behind countryman Hashim Amla in 150 innings.
De Kock, 32, is the fifth South African to score 7,000 or more ODI runs behind Jacques Kallis (11,550), AB de Villiers (9427), Amla (8113) and Herschelle Gibbs (8094).
De Kock and Pretorius set the platform with a 72-run opening stand before the spinners hit back for Pakistan as the visitors lost their nine wickets for 56 runs.
Agha dismissed Pretorius and Tony de Zorzi for two in the space of 15 runs before left-arm spinner Mohammad Nawaz ended all hopes of a big total with the wicket of De Kock in the 25th over.
Abrar jolted the innings by dismissing Rubin Hermann (one), Donovan Ferreira (seven) and Corbin Bosch (nought) in successive overs.
He then ended Breetzke's resistence-filled 16 to improve on his previous best of 4-33 which came against Zimbabwe in Harare last year.
Shaheen had Nqabayomzi Peter (16) and Lungi Ngidi (nought) to wrap up the innings in the 38th over.
(AFP)
