What is the Masnoon (Sunnat) way to trim nails and on which days
nails should not be trimmed?
A: The Masnoon (Sunnat) way of trimming nails is to start trimming nails from the index finger (Shahadat) of the right hand and work your way down to pinkie finger. Then proceed to the left hand starting from pinkie finger and finishing up at thumb. Finally the thumb of right hand should be trimmed. There is no sequence has been mentioned for feet nail trimming though it is better to use the same sequence used to do Khalal of feet (Start from the pinkie of right foot and finish it up at the thumb, then start from the thumb of left foot towards pinkie). Same is mentioned in Bahare Shariat (part 16, page 196) and Fatawae Alamgeri (part 5, page 358), *1. There is no prohibition regarding the days to avoid trimming nails. Whichever day the nails are trimmed on is Masnoon because there is no proven Hadis about prescribed days. But in some Zaeef (weak) Ahadees Wednesday is prohibited for trimming nails. Therefore if Wednesday is the day of Wajoob (Wajib to perform nail trimming). For example if a person has not trimmed nails for 39 days and 40th day is on Wednesday and if he/she does not trim nails on Wednesday than 40 days would be completed. Then it will be Wajib on him/her to trim nails on Wednesday because it is prohibited and Makrooh-e-Tehreemi to exceed 40 days without trimming nails.
Allah Tala Knows The Best.