diff --git a/docs/topics/signals.rst b/docs/topics/signals.rst
index 97be46f2a..02fa6e287 100644
--- a/docs/topics/signals.rst
+++ b/docs/topics/signals.rst
@@ -163,7 +163,7 @@ bytes_received
 --------------
 
 .. signal:: bytes_received
-.. function:: bytes_received(data, request, spider, source)
+.. function:: bytes_received(data, request, spider)
 
     Sent by the HTTP 1.1 and S3 download handlers when a group of bytes is
     received for a specific request. This signal might be fired multiple
@@ -180,10 +180,6 @@ bytes_received
     :param spider: the spider associated with the response
     :type spider: :class:`~scrapy.spiders.Spider` object
 
-    :param source: a string to identify which handler sent the signal
-        (current values could be "http11" or "s3")
-    :type source: :class:`str` object
-
 spider_closed
 -------------
 
diff --git a/scrapy/core/downloader/handlers/http11.py b/scrapy/core/downloader/handlers/http11.py
index c350cd3c2..bda21b6b9 100644
--- a/scrapy/core/downloader/handlers/http11.py
+++ b/scrapy/core/downloader/handlers/http11.py
@@ -33,9 +33,8 @@ logger = logging.getLogger(__name__)
 class HTTP11DownloadHandler:
     lazy = False
 
-    def __init__(self, settings, crawler=None, source="http11"):
+    def __init__(self, settings, crawler=None):
         self._crawler = crawler
-        self._source = source
 
         from twisted.internet import reactor
         self._pool = HTTPConnectionPool(reactor, persistent=True)
@@ -71,8 +70,8 @@ class HTTP11DownloadHandler:
         self._disconnect_timeout = 1
 
     @classmethod
-    def from_crawler(cls, crawler, **kwargs):
-        return cls(crawler.settings, crawler, **kwargs)
+    def from_crawler(cls, crawler):
+        return cls(crawler.settings, crawler)
 
     def download_request(self, request, spider):
         """Return a deferred for the HTTP download"""
@@ -83,7 +82,6 @@ class HTTP11DownloadHandler:
             warnsize=getattr(spider, 'download_warnsize', self._default_warnsize),
             fail_on_dataloss=self._fail_on_dataloss,
             crawler=self._crawler,
-            source=self._source,
         )
         return agent.download_request(request)
 
@@ -281,7 +279,7 @@ class ScrapyAgent:
     _TunnelingAgent = TunnelingAgent
 
     def __init__(self, contextFactory=None, connectTimeout=10, bindAddress=None, pool=None,
-                 maxsize=0, warnsize=0, fail_on_dataloss=True, crawler=None, source=None):
+                 maxsize=0, warnsize=0, fail_on_dataloss=True, crawler=None):
         self._contextFactory = contextFactory
         self._connectTimeout = connectTimeout
         self._bindAddress = bindAddress
@@ -291,7 +289,6 @@ class ScrapyAgent:
         self._fail_on_dataloss = fail_on_dataloss
         self._txresponse = None
         self._crawler = crawler
-        self._source = source
 
     def _get_agent(self, request, timeout):
         from twisted.internet import reactor
@@ -430,7 +427,6 @@ class ScrapyAgent:
                 warnsize=warnsize,
                 fail_on_dataloss=fail_on_dataloss,
                 crawler=self._crawler,
-                source=self._source,
             )
         )
 
@@ -468,9 +464,7 @@ class _RequestBodyProducer:
 
 class _ResponseReader(protocol.Protocol):
 
-    def __init__(
-        self, finished, txresponse, request, maxsize, warnsize, fail_on_dataloss, crawler, source
-    ):
+    def __init__(self, finished, txresponse, request, maxsize, warnsize, fail_on_dataloss, crawler):
         self._finished = finished
         self._txresponse = txresponse
         self._request = request
@@ -483,7 +477,6 @@ class _ResponseReader(protocol.Protocol):
         self._bytes_received = 0
         self._certificate = None
         self._crawler = crawler
-        self._source = source
 
     def connectionMade(self):
         if self._certificate is None:
@@ -503,7 +496,6 @@ class _ResponseReader(protocol.Protocol):
             data=bodyBytes,
             request=self._request,
             spider=self._crawler.spider,
-            source=self._source,
         )
 
         if self._maxsize and self._bytes_received > self._maxsize:
diff --git a/scrapy/core/downloader/handlers/s3.py b/scrapy/core/downloader/handlers/s3.py
index 2366b6394..40a1fa48e 100644
--- a/scrapy/core/downloader/handlers/s3.py
+++ b/scrapy/core/downloader/handlers/s3.py
@@ -73,7 +73,6 @@ class S3DownloadHandler:
             objcls=httpdownloadhandler,
             settings=settings,
             crawler=crawler,
-            source="s3",
         )
         self._download_http = _http_handler.download_request
 
diff --git a/tests/test_engine.py b/tests/test_engine.py
index 26f3163cf..acfe94f63 100644
--- a/tests/test_engine.py
+++ b/tests/test_engine.py
@@ -112,7 +112,6 @@ class CrawlerRun:
         self.itemerror = []
         self.itemresp = []
         self.bytes = defaultdict(lambda: list())
-        self.bytes_source = set()
         self.signals_caught = {}
         self.spider_class = spider_class
 
@@ -166,9 +165,8 @@ class CrawlerRun:
     def item_scraped(self, item, spider, response):
         self.itemresp.append((item, response))
 
-    def bytes_received(self, data, request, spider, source):
+    def bytes_received(self, data, request, spider):
         self.bytes[request].append(data)
-        self.bytes_source.add(source)
 
     def request_scheduled(self, request, spider):
         self.reqplug.append((request, spider))
@@ -281,7 +279,6 @@ class EngineTest(unittest.TestCase):
 
     def _assert_bytes_received(self):
         self.assertEqual(9, len(self.run.bytes))
-        self.assertEqual(self.run.bytes_source, set(["http11"]))
         for request, data in self.run.bytes.items():
             joined_data = b"".join(data)
             if self.run.getpath(request.url) == "/":