What does this verse mean ? Also specify the exact location of the verse?
Well this verse is present in both Śrī Liṅga Mahāpurāṅam and Śrī Saura Purāṅam.
🌼 From Shri Linga Mahapurana :
अन्यभक्तसहस्रेभ्यो विष्णुभक्तो विशिष्यते ॥ विष्णुभक्तसहखेभ्यो रुद्रभक्तो विशिष्यते। रुद्रभक्कात्परतरो नास्ति लोके न संशयः ॥
~ Linga Purana, 2.4.19b-20
A devotee of Viṣṇu greater than thousands of other devotees. A devotee of Rudra is far better than thousands of devotees of Viṣṇu. There is certainly no one greater than the devotee of Rudra in this world .
🌼 From Sri Saura Purana :
सूर्यवह्नीन्दुभक्तानामुत्तमो वैष्णवः परः ॥ वैष्णवानां सहस्रेभ्यः शिवभक्तो विशिष्यते ।
~ Sri Saura Purana, 11.8b-9a
The worshiper of Vishnu is superior to the worshipers of Surya, Agni and Chandra. A Shiva devotee is greater thousands of Vishnu devotee.