The ruling on concluding the prayer with Surat al-Ikhlas

Question : The man whom the Prophet (peace and blessings be upon him) appointed over a secret mission; he sent him on a secret mission and made him its commander. He used to recite and conclude the prayer for them with "Say: He is Allah, the One," and the Prophet (peace and blessings be upon him) approved that for him.

Answer : However, he did not tell the community, "When you pray, conclude with 'Say: He is Allah, the One,'" and he (peace and blessings be upon him) did not do it himself either. This indicates that it is not prescribed, but it is permissible and there is no harm in it.