Getting toast message with text sending I'm using Asus 551 with lollipop. I have numerous apps installed. Recently, I started getting toast notification with the text Sending....

This usually occurs when I'm using Facebook, whatsapp and such apps. It seems fishy. 

I recently uninstalled es file explorer after a similar issue was reported by users. It was showing similar toast with some Chinese text.

Is there a way I could find out what app is causing this?

Here is a screen shot:



I tried the dumpsys command, as suggested by @Firelord. Then used some of the apps, got the Sending... toast a couple of times, then again ran the dumpsys command, but there was no difference in the log. Here is how it looked before and after:
Turns out that it was the Sim ToolKit that was showing the toast notification. I have recently switched to a Reliance Jio Sim (India), which has free unlimited calls and 4G data until December! Now that is too good to believe and fishy.

I used this app: https://play.google.com/store/apps/details?id=com.coconuts.pastnotifications&amp;hl=en
And allowed it to monitor the Toasts via Accessibility settings.

For now I have Force Stopped the process. The toasts are gone, should they come back, I will disable the Jio Sim itself.