ħattuta ħattuta qaṣṣaṛ ʕṃəṛha, akəṃṃus n xer i ənšni, akəṃṃus n šaṛ i ntnənThe first part of this is in Arabic, and is not too different from what you might hear elsewhere in Egypt: ħattuta ħattuta is a corruption of حدوتة ħadduta, Egyptian Arabic for "story". (For similar formulae in Palestinian tales, such as tūtū tūtū faraɣat il-ħaddūtu, see Sirhan 2014.) The second part is in Berber, and hence presumably has an older history within Siwi; it is precisely paralleled in an opening formula used at Ouargla (Algeria):
Hattuta hattuta its span has shortened[Ar], bundle of good for us, bundle of bad for them
Ṛəbbi yəttamən f lxiṛ ụhụ f ššəṛṛ, lxiṛ nn-iw, ššəṛṛ nn-əs, ini yiwi-tən gaɛBasset (1920:107) places this formula in a wider context; throughout the Berber world, opening or closing formulae commonly take the form of "propitiatory formulae or formulae for the expulsion of evil", which he takes to indicate that the act of storytelling must have been viewed as potentially dangerous. Alongside Ouargla, he cites Kabyle examples blessing the group and cursing the jackal, and Shilha ones wishing the teller the meat and the others the tripes. The Siwi formula, however, is far closer to the Ouargla one than to anything else Basset mentions. And whereas the Kabyle formula invokes an animal whose importance in Berber folklore and mythology is obvious, and the Shilha one remians close to everyday life, all the key words of the Ouargli and Siwi formulae are specifically Arabic and religious (Rabbī "my Lord", khayr "good", sharr "bad"). This suggests that, while the idea may be Berber, the formulation itself might be taken from Arabic.
God believes(?) in good not in bad; the good for me, the bad for him, or may He take them both
As it happens, the early Islamic period furnishes us with just such a formula in Arabic, in a similar but curiously different context. The still widely used Interpretation of Dreams, attributed to Ibn Sirin, explains in its introduction that a dream interpreter who does not want to reveal his interpretation to his client should instead tell him the following: "May good be for you and bad be for your enemies; may you receive good and avoid bad" (خير لك وشر لأعدائك، خير تؤتاه وشر تتوقاه), or, if the interpretation concerns the interpreter too: "May the good be for us and the bad be for our enemies (etc.)" This expression is also found in an unmistakeably related context in some dubious hadiths reporting Umar ibn al-Khattab as saying "Learn to read the Qur'an in Arabic, and the interpretation of dreams, and say: May good (khayr) be for us and bad (sharr) for our enemy", and: "If one sees a vision and recounts it to one's brother, let him say: May good be for us and bad for our enemy".
The obvious interpretation is that, at some point in the early history of these Saharan oases, the act of telling tales was locally assimilated to the act of recounting dreams, allowing the Arabic formula for the latter to be adopted for the former. It would be interesting to know why this happened; was the idea that a tale, no less than a dream, somehow contained cryptic clues about the future? Or did Saharan Berbers in late antiquity make a habit of recounting dreams to one another on winter evenings, as well as folktales? Unfortunately, we'll probably never know for sure, but it can be interesting to speculate...