WhatsApp quietly introduced read receipts (letting people see exactly when a message is read, not just delivered) earlier this month.
WhatsApp has introduced the option to disable it.The update, however, is available only to Android users who have downloaded the new beta version of the app.

The first step is to get the latest APK file from WhatsApp:

Download the latest (version 2.11.448) WhatsApp apk from the official website.

On your Android phone, go to Settings > Security > Check Unknown sources, to enable installing apps from outside Google Play. Note that the exact path to the setting can vary depending on your device manufacturer and Android version – the important thing to note is that you enable installing apps from unknown sources.

Open the apk on your Android phone. This will install the latest version of the app on your device.
Once the app is installed, here’s how to disable read receipts:

Open WhatsApp and tap three vertical dots icon on the top right.

Now go to Settings > Account > Privacy.

Uncheck Read receipts.