‘Ali ibn Abi Tālib (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "There is no orphanhood after reaching puberty, and there is no silence for the whole day till the night."
Firstly as person is not legally considered an orphan after reaching puberty. Secondly, in the pre-Islamic period people used to commit themselves to silence for an entire day and night as an act of worship. A person would stay silent without speaking all day at all until sunset. Muslims were prohibited from this because this necessitates leaving many worships of Allah like not glorifying Allah by making Tasbīh (saying "Subhān Allah"), or declaring Allah’s Oneness by making Tahlīl (saying "there is no god but Allah"), or praising Him by making Tahmīd (saying "praise be to Allah"), or by enjoining good and forbidding evil, reading the Qur'an, and so forth. This is from the practices of the period of pre-Islamic ignorance and this is another reason why Islam prohibited this practice.