How to send whatsapp messages without saving number?
You will need to do the following trick

https://api.whatsapp.com/send?phone=xxxxxx

Copy this and paste it on your browser, please replace "xxxxxx" with the phone number (with country code but without +. Example= https://api.whatsapp.com/send?phone=901234567890), then hit enter. This will redirect you to WhatsApp and you will begin to talk to contact without saving the phone.