It was during South Africa's 32nd over of the innings that Ashwin injured himself (side strain) while diving to his right off his own bowling to stop the ball. The spinner, in his 100th ODI, walked off the field after 3.4 overs with figures of 1/10.
There were concerns over his participation for the rest of the match as a bowler but he put them to rest and returned to field. However, he was not allowed to bowl right away by on-field umpires Aleem Dar of Pakistan and India's Vineet Kulkarni as per the International Cricket Council's (ICC) rules.
According the ICC ODI Playing Conditions, a player has to spend the same amount of time on the field for which he was not on it. Ashwin was off the field for 25 minutes. He was allowed to bowl from 11.55 AM local time. He had returned to the ground at the start of the 38th over.
Ashwin came on to bowl the 43rd over after having spent 25 minutes as a fielder. However, he bowled just 1 over and walked out again (1/14 in 4.4 overs), as doubts resurfaced for the next match and the series.
This rule applies in case of internal injury. For injuries sustained on the field of play, a bowler or batsman is allowed to resume his duties immediately. Ashwin's injury fell in internal category.
For the full understanding of the ICC rule, read the following
2.2 Law 2.5 - Fielder absent or leaving the field
Law 2.5 shall be replaced by the following:
If a fielder fails to take the field with his side at the start of the match or at any later time, or leaves the field during a session of play, the umpire shall be informed of the reason for his absence, and he shall not thereafter come on to the field during a session of play without the consent of the umpire. (See Law 2.6 as modified). The umpire shall give such consent as soon as practicable.
If the player is absent from the field for longer than 8 minutes:
2.2.1 the player shall not be permitted to bowl in that innings after his return until he has been on the field for at least that length of playing time for which he was absent.
2.2.2 the player shall not be permitted to bat unless or until, in the aggregate, he has returned to the field and/or his side's innings has been in progress for at least that length of playing time for which he has been absent or, if earlier, when his side has lost five wickets.
The restriction in clauses 2.2.1 and 2.2.2 above shall not apply if the player has suffered an external blow (as opposed to an internal injury such as a pulled muscle) whilst participating earlier in the match and consequently been forced to leave the field. Nor shall it apply if the player has been absent for very exceptional and wholly acceptable reasons (other than injury or illness).