Whenever Sayyiduna Ali (may Allah be pleased with him) touched the Black Stone, he would say: 'Allahumma imanan bika, wa tasdiqan bi-kitabika, wa ittiba'an li-sunnati nabiyyika (peace and blessings be upon him)' (O Allah, believing in You, affirming the truth of Your Book, and following the Sunnah of Your Prophet (peace and blessings be upon him) (I touch this)).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9252