SB 3.4.24

sa taṁ mahā-bhāgavataṁ
 vrajantaṁ kauravarṣabhaḥ
viśrambhād abhyadhattedaṁ
 mukhyaṁ kṛṣṇa-parigrahe
saḥ — Vidura; tam — unto Uddhava; mahā-bhāgavatam — the great devotee of the Lord; vrajantam — while going; kaurava-ṛṣabhaḥ — the best amongst the Kauravas; viśrambhāt — out of confidence; abhyadhatta — submitted; idam — this; mukhyam — unto the chief; kṛṣṇa — Lord Kṛṣṇa; parigrahe — in devotional service to the Lord.
While Uddhava, the chief and most confidential amongst the devotees of the Lord, was going away, Vidura, in affection and confidence, questioned him.

Vidura was much older than Uddhava. By family relationship Uddhava was a contemporary brother of Kṛṣṇa’s, while Vidura was as elderly as Kṛṣṇa’s father Vasudeva. But although junior by age, Uddhava was much advanced in the devotional service of the Lord, and therefore he is described herein as the chief amongst the devotees of the Lord. Vidura was confident about this, and thus he addressed Uddhava in that higher category. That is the way of courteous dealings between two devotees.