Imām Muḥammad ibn Ṣāliḥ al-ʿUthaymīn (d. 1421 AH) said:

[Q]: Does the obligation of washing the dead encompass miscarried foetuses?

[A]: This matter requires elaboration. If the soul of life has been breathed into it, then it should be washed, embalmed, and prayed upon. If the soul of life has not been breathed into it, then it is not washed.

The soul of life is breathed into the foetus after a period of four months. The evidence for this is the ḥadīth of ʿAbdullāh ibn Masʿūd (رضي الله عنه) who said: The Messenger of Allāh (صلى الله عليه وسلم) narrated to us, and he is the truthful, the verified: “Indeed, the creation of each one of you is orchestrated in the wombs of your mother spending forty day as a drop, then as a clot for an equal period, then a small lump of flesh for an equal period. Then an angel is sent to it and ordered with four articles: to write his provision, his length of life, his deeds, and whether he will be from among the happy or the sad [i.e., denizens of Paradise or Hell], then the soul of life is breathed into him.”¹ The Prophet (صلى الله عليه وسلم) cannot know such matters except by means of revelation, as this type of issue is not one of opinion.

Endnotes:
[1] Authentic: narrated by al-Bukhārī: 6594 and Muslim: 2643

Source: Al-Sharḥ al-Mumtiʿ 1: 343
Translated by: Riyāḍ al-Kanadī