A purchase and sale agreement between authorized persons for each entity should be sufficient. Note that technically the LLC is the owner of the property. If you're trying to gift property from one person to another, the LLC relationship may be examined. Why would LLC A want to gift property to LLC B? This doesn't sound like a business relationship but a deal that revolves solely around the personal. If it appears that the LLCs are just alter egos for yourself and your partner to avoid liabilities then you may run into issues - especially with the IRS.
Especially with regard to real estate transfers, it is highly advisable for you to obtain a proper legal consultation with a licensed real estate and/or tax attorney. Real estate sales are typically large in size and much more likely to be subject to scrutiny, such as by the IRS.
