Extract out the commit hash, then build up your search from there. EG:
sourcetype=my_log example.com:9491 (131269 or Replication )| rex field=_raw "^.*\[(?<commit_hash>\w.*?)\]" | stats values(_raw) by commit_hash
This should return something like this (
| commit_hash | _raw
6d230057 | 2015-11-26 22:40:25,394 [] scheduled test:refs/changes/69/131269/1 to [6d230057] push http://user@exam
| 2015-11-26 22:40:30,394 [6d230057] Replication to http://user@example.com:9441/test/abc.git started...
| 2015-11-26 22:40:33,293 [6d230057] Replication to http://user@example.com:9441/test/abc.git completed in
2d7bc846 | 2015-11-26 22:40:25,395 [] scheduled test:refs/changes/69/131269/1 to [2d7bc846] push http://user@example
| 2015-11-26 22:40:30,395 [2d7bc846] Replication to http://user@example.com:9491/test/abc.git started...
| 2015-11-26 22:40:32,334 [2d7bc846] Replication to http://user@example.com:9491/test/abc.git completed i
pipe a search in after stats if you want to filter down further. You shouldn't need a subsearch
See http://docs.splunk.com/Documentation/Splunk/6.3.1/SearchReference/Rex for more details on rex
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