Muwatta Malik · Hadith 405

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ نَافِعٍ، أَنَّ عَبْدَ اللَّهِ بْنَ عُمَرَ، كَانَ يَقُولُ إِذَا لَمْ يَسْتَطِعِ الْمَرِيضُ السُّجُودَ أَوْمَأَ بِرَأْسِهِ إِيمَاءً وَلَمْ يَرْفَعْ إِلَى جَبْهَتِهِ شَيْئًا ‏.‏

Yahya related to me from Malik from Nafi that Abdullah ibn Umar used to say, "When a sick man is unable to prostrate he should motion with his head, and not raise anything to his forehead

Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).