I have heard this colloquially but I would like to be pointed to a reference in the Hadith for the notion that "every spot that we do Sajdah at on this Earth, will testify for us on the Day of Judgment; it will emit light on that Day for us"
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I could not find a hadith with those exact words, but this is inferred in later texts. Also, there is a supporting hadith .
Ar-Ramli said in Nihaayat al-Muhtaaj (1/552): It is Sunnah to move in order to offer a naafil or obligatory prayer from the place where one offered an obligatory or naafil prayer, so as to increase the number of places where one prostrates, for they will testify in one’s favour, and because that means filling more spots with worship. And if one does not move to another spot, then one should separate the prayers by speaking to someone. 
 I could not find a hadith with those exact words, but this is inferred in later texts. Also, there is a supporting hadith .