WhatsApp limits the number of contacts to whom messages can be sent each day (every 24 hours) according to the account rating, however it does not limit the number of messages that can be sent to each contact.
WhatsApp rates each account according to four levels of sending:
Tier 1 – Sending to up to 1,000 contacts per day (each new account)
Tier 2 – Sending to up to 10,000 contacts per day
Tier 3 – Sending to up to 100,000 contacts per day
Tier 4 – Sending an unlimited number of messages.
Each new account starts from the first level (Tier 1) and moves up to the next level automatically as the number of messages it sends increases and its positive reputation is maintained.
*This limitation does not exist in case the contact person starts the conversation.