Vaishnava Samhita. Shri Vyasadasa Charitam I. Vol II Book VI Chp 2 Shlokas 26 - 28

व्यासदास उवाच 

उपवीतञ्च सफलं ब्रह्मण्यं सफलञ्च मे 
एतदर्थं हि धर्तव्यमुपवीतं तु वैष्णवैः   ||

निमग्नानां तु साधूनां कृष्ण लीलारसाम्बुधौ 
लौकिकं वैदिकं कर्तुमवकाशो न विद्यते   ||

सन्ध्यावन्दनहीनस्य त्यक्तसर्वक्रियस्य मे 
अतीतलोकदेवस्य यज्ञसूत्रेण किं फलम्   ||

Vyasadasa said

My sacred thread became invaluable today. My birth as a brahmana became meaningful today. Vaishnavas like me should wear the sacred thread for this purpose only. Sadhus who have drowned deep into the exhilarating ocean of Shri Krishna's pastimes find no time to perform earthly and the Vedic rituals. What benefit do I get in wearing this sacred thread? I have given up the day-to-day ritualistic routine and all other religious rites. I stand beyond the Vedic rules and obligations of worldly life.