No conveyance in writing of lands shall be defeated nor any estate encumbered by an agreement unless it is inserted in the condition of the conveyance and made part thereof, stating the sum of money to be secured, or other thing to be performed.
RSA 479:2
RS 131:2. CS 137:2. GS 122:2. GL 136:2. PS 139:2. RL 215:2. RL 261:2.