من لا يحضره الفقيه, volume 2, page 87

Hadith.1806 - It is narrated from Imam Musa ibn Jafar Al-Kadhim (as) who said: "Whoever fasts the first day of the ten days of Dhu al-Hijjah, Allah (swt) will record for him the reward of fasting eighty months. And if he fasts all nine days, Allah (swt), the Almighty, will record for him the reward of fasting a lifetime."

Translation: Bab Ul Qaim Publications·Thaqalayn link·The Arabic above is the original.

Hadith.1807 - Imam Jafar ibn Muhammad Al-Sadiq (as) said: "Fasting on the Day of Tarwiyah is an expiation for one year, and fasting on the Day of Arafah is an expiation for two years."

Translation: Bab Ul Qaim Publications·Thaqalayn link·The Arabic above is the original.

Hadith.1808 - It is narrated: "On the first day of Dhu al-Hijjah, Ibrahim, the Friend of the Most Merciful (as), was born. Whoever fasts on that day, it will be an expiation for sixty years. On the ninth of Dhu al-Hijjah, the repentance of Dawud (as) was accepted. Whoever fasts on that day, it will be an expiation for ninety years."

Translation: Bab Ul Qaim Publications·Thaqalayn link·The Arabic above is the original.

Hadith.1809 - It is narrated from Ya‘qub ibn Shu‘ayb, who said: I asked Abu Abdullah (Imam Jafar ibn Muhammad Al-Sadiq (as)) about fasting on the Day of Arafah. Imam (as) said: 'If you wish, you may fast, and if you wish, you may refrain from fasting.' Imam (as) mentioned: 'A man came to al-Hasan (as) and al-Husayn (as) and found one of them fasting and the other not fasting. He asked them, and they said: "If you fast, it is good, and if you do not fast, it is permissible."’"

Translation: Bab Ul Qaim Publications·Thaqalayn link·The Arabic above is the original.

Hadith.1810 - It is narrated by Abdullah ibn al-Mughira from Salim, from Abu Abdullah (Imam Jafar ibn Muhammad Al-Sadiq (as)), who said: "The Messenger of Allah (swt) (peace and blessings be upon him and his family) bequeathed solely to Ali (as), and Ali (as) bequeathed jointly to al-Hasan (as) and al-Husayn (as). Al-Hasan (as) was the Imam during his time. A man entered upon al-Hasan (as) on the Day of Arafah and found him having lunch, while al-Husayn (as) was fasting. After al-Hasan (as) passed away, the same man entered upon al-Husayn (as) on the Day of Arafah and found him having lunch, while Ali ibn al-Husayn (as) was fasting. The man said to Imam: 'I came to al-Hasan (as) when he was having lunch, and you were fasting. Then I came to you, and now you are not fasting.' Imam (as) replied: 'Al-Hasan (as) was the Imam, so he broke his fast to ensure his fasting would not be taken as a Sunnah and followed by others. When he passed away, I became the Imam, and I did not want my fasting to be taken as a Sunnah and followed by others.'"

Translation: Bab Ul Qaim Publications·Thaqalayn link·The Arabic above is the original.