"Ajmal pleaded guilty to a Level 1 breach of the ICC Code of Conduct during the third day's play on Friday," the International Cricket Council (ICC) said.
Ajmal, 36, was found to have breached an article of the code of conduct which relates to "using language or a gesture that is obscene, offensive or insulting during an international match".
"The incident happened when Ajmal, after dismissing South Africa batsman Morne Morkel, turned to the umpire and repeatedly appealed even though the batsman had been caught at first slip by Younis Khan.
Ajmal took 6-151 in South Africa's total of 517. Pakistan resumed the fourth day (Saturday) facing a heavy defeat at 132-4.