Timestamp field must to stored to get returned

timestamp.sh

curl -XDELETE 'localhost:9200/test'

curl -XPUT 'localhost:9200/test/' -d '
{
    "mappings" : {
        "_default_": {
            "_timestamp" : { "enabled" : true, "store" : true }
        }
    }
}
'


curl -XPUT 'localhost:9200/test/doc/1' -d '
{
    "sentence" : "Hi!",
    "value" : 1
}
'

curl 'localhost:9200/test/_refresh'


curl -XPOST 'localhost:9200/test/_search' -d '
{
     "query" : {
        "match_all" : {
        }
     },
     "fields" : [ "_timestamp" ]
}
'