وَعَنْ عَلِيٍّ رَضِيَ اللَّهُ عَنْهُ قَالَ: كَانَ لِي مِنْ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مَدْخَلٌ بِاللَّيْلِ وَمَدْخَلٌ بِالنَّهَارِ فَكُنْتُ إِذَا دخلتُ بِاللَّيْلِ تنحنح لي. رَوَاهُ النَّسَائِيّ
Ali (may Allah be pleased with him) narrates: I had permission to visit the Messenger of Allah (peace and blessings be upon him) at night and during the day. When I would go at night, he (peace and blessings be upon him) would cough for me (as a sign of permission). Chain is weak, narrated by Al-Nasa'i.