“Al-Tabarani narrated it with a good, strong chain of transmission.”

Al-Haythami said (8/276):

“...its narrators are those of the Sahih, apart from al-Muʿafa ibn Sulayman, who is trustworthy.”

In al-Jami al-Kabir, the hadith is attributed to al-Bayhaqi! I believe this is a corruption of an attribution to al-Tabarani. And Allah knows best.

3274—“Abu al-Sanabil has spoken falsely; it is not as he said. You are now free to marry, so marry. [If someone comes to you whom you approve of, come to me, or let me know.]” He said this to Subayʿah bint al-Harith, who gave birth a few days after her husband’s death.

Saʿid ibn Mansur recorded it in his Sunan (2/350/1506): Sufyan narrated to us, from al-Zuhri, from ʿUbayd Allah ibn ʿAbd Allah [ibn ʿUtbah], from his father:

Subayʿah bint al-Harith recovered from her postnatal bleeding (1) a few days after her husband’s death. Abu al-Sanabil passed by her and said, “You may not marry (!) until you have waited four months and ten days.” She mentioned this to the Messenger of Allah, and he stated the hadith, without the additional wording.

Al-Shafiʿi likewise narrated it in al-Umm (5/206): Sufyan ibn ʿUyaynah narrated to us, with this chain; except that he added “or,” saying, “Or is it not ...?”

Al-Bayhaqi likewise narrated it from al-Shafiʿi in al-Sunan (7/429), as did al-Baghawi in Sharh al-Sunnah (9/304/2388) and al-Tafsir (8/153). Al-Bayhaqi said:

“This version is mursal, whereas the connected reports preceding it are sufficient.”