As an individual, you don't have the authority to unilaterally declare something in the public domain, especially if it is a traditional proverb with unclear authorship. The public domain status usually comes about through expiration of copyright or intentional dedication by the copyright holder. Proverbs and folk wisdom often exist in the public domain due to their age and widespread use over time. If you're referring to this proverb in a specific work, it's advisable to clarify the usage and attribution appropriately.