Halakha Ulangan 34:8: Kitzur Shulchan Arukh & Shulchan Arukh, Yoreh De'ah

It is forbidden to grieve excessively over the dead, as it is said, "Do not weep for the dead, and do not bemoan him."¹Jeremiah 22:10. Our Sages of blessed memory, said,²Masechess Moed Kattan 27b. "Is it possible to say so? But it means, "Do not weep for the dead excessively, and do not bemoan him inordinately." How should one mourn? Three days are appropriate for weeping, seven days for mourning, and thirty days for abstaining from wearing ironed clothes, and from having the hair cut. Thereafter the Holy One, blessed is He, says, "You are not permitted to show him more compassion than I do." Our Sages, of blessed memory, said,³Ibid. "One who grieves excessively over the dead, will have cause to weep over another death." This applies only when the deceased was an ordinary person, but if he was a Torah scholar, he is mourned in proportion to his wisdom. Nevertheless, you should not weep over him more than thirty days, for he is not greater than Moshe Rabbeinu, peace unto him, of whom it is written, "And the Children of Yisrael wept for Moshe thirty days."⁴Deuteronomy 34:8.

This applies to the rest of the people, but [as to] scholars [who died], everything is according to their wisdom;³Tur citing RaShBA. and one does not weep for them more than thirty days,⁴Derived from Rabbi’s instructions prior to his death, viz., ‘Reassemble the College after thirty days for I am not more important than Moses of whom it is written, “And the children of Israel wept for Moses in the plains of Moab thirty days”’ (Deut. XXXIV, 8) — Ket. 103b. nor does one make a lamentation for them more than twelve months,⁵Ket. ibid. and likewise, a Sage whose [death] report was received after twelve months, is not lamented.⁶Yeb. 79a. Cf. M.K. 21b. This applies even on the day that the death report is received — Shak.