It is reported that Shurayḥ the Judge used to have a house in which he would spend time alone on Fridays; no one knew what he did in it.

Al-Dhahabī, Siyar A’lām Al-Nubalā` Vol.4 p105.

It is reported that Abū Al-‘Āliyah said, “I learned writing and the Qur`ān without my family noticing, and not a drop of ink was ever seen on my garment.”

Abū Nu’aym, Ḥilyatu Al-Awliyā` Vol. 2 p217.

It is reported that when Ibn Abī Laylā prayed [at night], if someone entered [his house], he would lie down on his bed [as if he was sleeping].

Ibid. Vol. 4 p351.

It is reported that Ayyūb Al-Sakhtiyānī used to pray all night and hide it. In the morning, he would raise his voice as if he had just woken up.

Al-Dhahabī, op. cit. Vol. 6 p17.

It is reported that Dāwūd b. Abī Hind fasted for forty years without his family knowing, he would take his lunch out with him and donate it in the street.

Ibid. Vol. 6 p378.