In any action, suit, or proceeding by or against any surviving partner or joint contractor, no adverse party or person adversely interested in the event thereof is a competent witness to testify, by virtue of section 13-90-101, to any admission or conversation by any deceased partner or joint contractor, unless one or more of the surviving partners or joint contractors were also present at the time of such admission or conversation.
C.R.S. § 13-90-104
For the nature of the joint liability of the partnership, see §§ 7-60-111 and 7-60-115.