Is saying 'Ask forgiveness for him' behind a funeral permissible?

Primary text

Saying behind the funeral procession, 'Ask forgiveness for him' (*istaghfiru lah*), is disliked by Sa'id ibn al-Musayyib, Sa'id ibn Jubayr, Al-Hasan, Al-Nakha'i, our Imam (Ahmad), and Ishaq. Al-Awza'i considered it an innovation (*bid'ah*), and 'Ata' considered it a newly invented matter (*muhdathah*). Sa'id ibn al-Musayyib, while ill, forbade it, referring to the caller who chants, 'Ask forgiveness for him, may Allah forgive you.' Ibn 'Umar rejected this practice when he heard someone saying it behind a funeral, responding, 'May Allah not forgive you.'