It is reported that Shurayh 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-Dhahabî, Siyar A’lâm Al-Nubalâ` Vol.4 p105.

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

Abû Nu’aym, Hilyatu Al-Awliyâ` Vol. 2 p217.

It is reported that when Ibn Abî Laylâ 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 Ayyûb Al-Sakhtiyânî used to pray all night and hide it. In the morning, he would raise his voice as if he had just woken up.

Al-Dhahabî, op. cit. Vol. 6 p17.

It is reported that Dâwûd b. Abî 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.