a message that was identical to the main treatment, but did not refer to the Prophet. The first of these messages tests if simply receiving a simple moral appeal without any religious connotation affects repayment decisions. The second message tests, whether adding a credible source adds power to the impact of a religious message to shed light on the mechanics of religious discourse.

The results from these variations of the moral incentive message are reported in Appendix Table A.3. The effect sizes are identical for all three variations of the moral incentive condition. In theory, this could indicate that either customers already associated the moral appeal contained in the message with religion (and potentially with the Prophet), or that the pure moral statement was indeed sufficient to trigger repayment. To disentangle these competing hypotheses, we conducted a follow-up phone survey with a random sample of credit card customers. In this phone survey, the message with the standard Indonesian word for “injustice” and without reference to the Prophet was read to customers, who were then asked to indicate its source.<sup>34</sup> The vast majority of clients were not immediately aware of the religious origin of the message. When asked “Who do you think might have said this phrase?”, out of 5 given options, 77% chose “I don’t know,” whereas only 19% associated the phrase with religious figures or entities (including the bank itself). These findings suggest that the higher repayment rate was not due to an implicit religious association with the message. These results also corroborate the view that our sample is relatively secular; most clients did not immediately recognize the Islamic doctrine on non-repayment of debts.

The follow-up survey also clarifies the role of religiosity in explaining our effects. The survey asked subjects about the importance of religion and the rules of Shari’a, using a 1-5 Likert scale. It also asked customers to rank family, work, friends and religion in terms of importance in their life. Because of the survey’s small sample size, we cannot directly use this measure for individual-level heterogeneity of treatment effects.<sup>35</sup> Instead, we use it to construct province-level indicators of religiosity, splitting the sample in half according to the share of respondents who identified as very religious.<sup>36</sup> In the top half of provinces (according to this religiosity measure), the main (religious) moral message increased repayment rates by 21%. In the bottom half of provinces, there was still a large and significant 11% increase (with a p-value of 0.016). Finally, the effects of the non-religious version of the moral message were similar in provinces with higher and lower shares of religious respondents.

> 34None of the customers in this sample had previously received any of the moral incentive text messages.

> 35This survey was administered in total to 2,840 customers. Among them 2,273 are participants of our experiment, while 567 are other randomly selected customers of the bank that did not participate in the experiment.

> 36Customers are identified as very religious if they answered ”Extremely Important” to both the question about religion and the question about the rules of _Shari’a_ law, and if they ranked religion as the most important thing in their life among all the choices given.

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