What is the ruling on one who experiences frequent lapses in prayer due to involuntary external thoughts, and is it legislated for him to give charity on account of his prayer?

Humility (khushu') in prayer is important; it is the spirit of prayer. However, mere thoughts or a lack of humility do not necessitate the prostration of forgetfulness (sujood as-sahw) unless they lead to an addition, omission, or doubt [in the prayer]. The prayer is not invalidated by a lack of humility, but its perfection is diminished. The deficiency in obligatory prayers can be compensated by abundant supererogatory prayers, and good charity (sadaqah) compensates for deficiencies in acts of worship.