Sayyiduna Jabir (may Allah be pleased with him) said: When we went up to high ground we would say 'Allahu Akbar' (Allah is the Greatest), and when we went down to level ground we would say 'Subhan Allah' (Glory be to Allah).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10366