Sahih al-Bukhari
Oneness, Uniqueness of Allah (Tawheed) — Hadith #7537
إِذَا تَقَرَّبَ الْعَبْدُ مِنِّي شِبْرًا تَقَرَّبْتُ مِنْهُ ذِرَاعًا وَإِذَا تَقَرَّبَ مِنِّي ذِرَاعًا تَقَرَّبْتُ مِنْهُ بَاعًا أَوْ بُوعًا "
The chain (isnad) appears to be missing from this record. Under review.
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. 502)
إِذَا تَقَرَّبَ الْعَبْدُ مِنِّي شِبْرًا تَقَرَّبْتُ مِنْهُ ذِرَاعًا وَإِذَا تَقَرَّبَ مِنِّي ذِرَاعًا تَقَرَّبْتُ مِنْهُ بَاعًا أَوْ بُوعًا "
See also hadith 502.