Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 24


स तं महाभागवतं व्रजन्तं कौरवर्षभ: ।विश्रम्भादभ्यधत्तेदं मुख्यं कृष्णपरिग्रहे ॥ २४ ॥


sa taṁ mahā-bhāgavataṁvrajantaṁ kauravarṣabhaḥviśrambhād abhyadhattedaṁmukhyaṁ kṛṣṇa-parigrahe


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.