Zubayr bin al-Awwaan (radiyallaahu anhu) said:

Whoever is able to have for himself a righteous action (he kept) secret, then let him do so. Al-Zuhd of Abee Dawood (2/362).

Abu al-Aaliyah (rahimahullah) said:

The Companions of Muhammad said to me: Do not act for other than Allaah so that He entrusts you to the one for whom you acted. Al-Musannaf (7/207)

Ali bin Abi Taalib (radiyallaahu anhu) said:

No action diminishes with taqwa. And how can that which is accepted [by Allaah] diminish? Al-Ikhlaas of Ibn Abi al-Dunya (no. 4)

Note: Alluding to the verse (إنما يتقبل الله من المتقين), "Indeed, Allaah accepts from those with taqwa (piety, fear of Allaah)." (5:27)

Narrations through: Min Akhbaar al-Salaf al-Saalih of Zakariyyah bin Ghulam Qadir. Translated by Abu Iyaad (@abuiyaadsp). May Allaah reward the donator of the resource and grant him success. Ameen.