All systems of Hindu philosophy have sutra literature of their own like Brahma sutras, Sankhya Sutras, Yoga Sutras, etc. Some darshanas have more than one sutras. Though the sutras of Narada Maharshi are most popular Bhakti Sutras, the sutras of Sandilya are to the Bhakti doctrine, what Brahma Sutras are to the Vedanta philosophy. While Narada’s Sutras are Sadhana-oriented, those of Sandilya are more of academic and polemic nature.
Svapnesvara’s commentary, the earliest one on these Sutras, gives a nice exposition of the terse Sutras and also describes the dialectics involved in the Bhakti doctrine. It was published in for the first time in Sanskrit by BD Basu in 1861 and its English translation by EB Cowell was published first in 1878.
Bhakti Aphorisms of Sandilya - Swapneswara's Commentary in English - EB Cowell
Bhakti Aphorisms of Sandilya - Swapneswara's Commentary in Sanskrit - BD Basu
Sandilya Bhakti Sutra with Sandkrit Text with English Commentary by Bhaktiprajnan Yati