D. Sources in Scripture and Talmud for the obligation to show gratitude:

Moshe showing gratitude to the Nile and earth: The verse[1] records that G-d commanded Moshe to instruct to Aaron take the staff and stretch it over the river of Egypt in order to turn the water into blood. Rashi[2], based on the Midrash[3], explains that the reason for this is because the river had protected Moshe when he was thrown into it and therefore he could not be the one to cause it to be smitten with the plague of blood and the plague of frogs and it was rather smitten by his brother Aaron. The same applied regarding the plague of lice, that since Moshe was protected by the sand when it was used to bury the Egyptian that he killed, therefore he could not be the one to smite it, and it was rather smitten by his brother Aaron.[4] From here we learn of the obligation for one to show gratitude to someone who provided one with kindness and good, even if the item is inanimate and will not understand the gratitude that it is given. According to one Midrash[5], this gratitude shown to the river and earth was done at the request of Moshe, while according to a different Midrash[6] the gratitude was requested by Hashem himself.

Showing gratitude to the nation of Egypt: The verse[7] states, “And you shall not despise the Edomite because he is your brother and you should not despise the Egyptian because you were a citizen in their land.” Meaning, that despite the fact that the Egyptians did terrible things to the Jewish people such as throwing their male sons into the river, nevertheless, since they provided a place of lodging for them in a time of need, therefore, the third-generation of Egyptians shall be allowed to marry into the Jewish people [after conversion].[8] However, the nation of Amon and Moav are restricted from ever marrying into the Jewish people even after conversion, being that they showed ingratitude to the Jewish people despite their ancestor Lot having received kindness from Abraham.[9] From here is the source of the saying “do not throw a stick into the well you drank from.”[10]

Moshe showing gratitude to Yisro: The Midrash[11] states that when Hashem appointed Moshe to meet with Pharoah to ask him to send the Jewish people from Egypt, he replied that he cannot do so as he had received kindness from Yisro who had opened his house for him and he was with him like a son and whoever opens a home for his friend, his soul remains indebted towards him.

Moshe showing gratitude to Midyan: The Midrash[12] states that when G-d commanded Moshe to seek vengeance against Midyan, he pushed back against doing so under the clause that he had grown up in Midyan and it’s not proper for him to cause suffering to someone who did him good.

Showing gratitude to dogs: The verse[13] states that Treif meat shall be thrown to the dog. Rashi explains the reason the verse instructs one to give Treif meat to a dog is in order to show gratitude to the dogs who did not bark at the Jewish people during the Exodus, and hence G-d commanded that the dog be given its reward, as G-d does not withhold reward from any creature.

Showing gratitude to the donkey: The mitzvah of Peter Chamor, requires one to redeem a firstborn donkey for a sheep. The Talmud[14] asks as to why the firstborn donkey was excluded from all of the animals, as no such law exists regarding the firstborn horse or firstborn camel. Rebbe Eliezer replied in his second answer that it is because they had helped the Jewish people when they left Egypt, as there was not one Jew who do not leave without 90 donkeys carrying the silver and gold of Egypt.

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[1] Shemos 7:19

[2] Rashi Shemos 7:19

[3] Midrash Tanchuma Vaera 14 “Hashem told Moshe, that since the water had guarded him when he was thrown into the river and since the earth had guarded him when he killed the Egyptian, it is therefore not proper for it to be smitten by him and it was therefore smitten by his brother Aron.”; Shemos Raba 20:1 “Hashem said to my ship turn the river into blood. He replied that he cannot turn into blood as is there a person who drinks from a well and then throws a stone into it. Hashem replied to him that Aaron should go and turn it into blood. Why didn’t my Shiva smite it he said because he was thrown into the water and it did not damage him and therefore it was hit by Aaron.”

[4] Midrash Tanchuma Vaera 14

[5] Shemos Raba 20:1

[6] Midrash Tanchuma Vaera 14

[7] Devarim 23:8

[8] Rashi and Ramban Devarim ibid

[9] Ramban Devarim ibid

[10] Bava Kama 92b

[11] Midrash Raba 4:2

[12] Yalkut Shimoni Bamidbar 31

[13] Mishpatim 22:30

[14] Bechoros 5b