Martin Goodman, “Rome and Jerusalem” (2009)
“All Jewish sources of this period suggest that Jews took the ownership of slaves as entirely normal, apart from the Essenes who, according to Philo (“Prob.” or “That Every Good Man Is Free,” 79), ‘condemn slave owners as unjust in that they offend against equality, but still more as ungodly, in that they transgress the law of nature, which having given birth to all men equally and nourished them like a mother, makes of them true brothers, not in name but in reality’; Josephus also remarks that they did not own slaves, ‘since they believe that [slave ownership] contributes to injustice’.” (pp.218-219).
Gropp, D. (2003). The Samaria Papyri from Wadi Ed-Daliyeh: The Slave Sales. U.M.I (or his 1986 dissertation) and Dušek, J. (2007). Les manuscrits araméens du Wadi Daliyeh et la Samarie vers 450-312 av. J.-C. Leiden: Brill. (In any case, beside Wadi Daliyeh, there are Nabataean deads of sale, some documents from exilic period, Syriac, Aramaic, Elephantine, Greek, some lpapyri from Ptolemaic and later, Roman Egypt with “jewish” connections).
As for Qumran, the issue is a bit more contentious, though see e.g. Cross, Frank Moore, and Esther Eshel. “Ostraca from Khirbet Qumrân.” Israel Exploration Journal 47, no. 1/2 (1997): 17–28, or relevant parts from Baumgarte, J. M. and Milik, J. T. (1996). Qumran Cave 4: The Damascus Document (4Q266–73), Discoveries in the Judaean Desert 13, Oxford 1996, that presence of some slaves is entirely plausible, or Hirschfeld in Qumran in context, specially for Herodian period. There is likewise a tradition to read Essene´s principled opposition narrowly and in a specifc way (nisi fallor, Hezser in her monography has a paragraph on this as an introduction), but there is not much to go on, or how later characterizations (Philo, Jos.) hold up, given that the evidence & arguments for the presence of it are not exactly ironclad as well.