From Sahih Bukhari (Hadith 7537):
Narrated Abu Huraira:Perhaps the Prophet (ﷺ) mentioned the following (as Allah's Saying): "If My slave comes nearer to Me for a span, I go nearer to him for a cubit; and if he comes nearer to Me for a cubit; I go nearer to him for the span of outstretched arms. (See Hadith No)
Reference: Bukhari 7537