The Kitáb-i-Aqdas
191.remember how We nurtured thee by day and by night for service to the Cause   ¶184
In God Passes By, Shoghi Effendi refers to the fact that Bahá’u’lláh, Who was thirteen years older than Mírzá Yaḥyá, had counselled him and watched over his early youth and manhood.
Other Related References
Shoghi Effendi
God Passes By,   pp. 112-115, 163-182