getAllAccountLoggers(gaal) {server}
getAccountLoggers(gal) {name@domain|id}
addAccountLogger(aal) {name@domain|id} {logging-category} {debug|info|warn|error}
removeAccountLogger(ral) {name@domain|id} {logging-category}

So copy/paste for turning off would be:
zmprov ral
user@domain.com zimbra.soap
If you want to do it across the board for everyone you can modify /opt/zimbra/conf/log4j.properties.in and append:
logger.com.zimbra.soap=DEBUG
Levels are FATAL, ERROR, WARN, INFO, DEBUG; see
this section of the NE Guide.
Here are some of the pre-defined categories:
zimbra.misc
zimbra.pop
zimbra.imap
zimbra.index
zimbra.journal
zimbra.lmtp
zimbra.mailbox
zimbra.account
zimbra.replication
zimbra.security
zimbra.soap