Using Kali Linux behind Whonix in VirtualBox

 After adding Kali Linux and Whonix in VirtualBox, do the following:
(Updated: 23 January 2019)

1. Start Whonix VM
2. Update Whonix VM
3. Run Whonix Check
4. Change Network Settings of Kali to "Internal Network". Choose Whonix.
5. Boot Kali and change the network settings. (No need to set this since the gateway has a DHCP server. Just update /etc/resolv.conf in Kali)
1. #ifconfig eth0 10.152.152.11
2. #route add default gw 10.152.152.10
6. Open check.torproject.org in a browser in Kali 

Note that the same technique can be used with other operating systems, such as Windows XP.