दम्पत्योः पितापुत्रयोः भ्रातृऋणां चाविभक्तानां परस्परकृतमृणमसाध्यम् ॥ कZ_०३.११.२१ ॥
dampatyoḥ pitāputrayoḥ bhrātṛṛṇāṃ cāvibhaktānāṃ parasparakṛtam ṛṇam asādhyam
Between spouses, between father and son, and among undivided brothers, a debt contracted by one against the other is not maintainable (not enforceable as a recoverable claim).
To prevent collusion and fragmentation of joint household property through strategic lawsuits, and to keep internal family accounting outside state enforcement.